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Sergeant Sidonus is a supporting protagonist of Warhammer 40,000: Space Marine. He is a grizzled veteran sergeant Space Marine of the Ultramarines Chapter, who fought to save planet Graia from an Ork WAAAGH!, and then fought against the subsequent Chaos invasion led by Chaos Lord Nemeroth. Until his death in late M41, Sidonus served as second-in-command of the Ultramarines 2nd Company, under his closest friend and confidant Titus.
Sidonus was voiced by Richard Hawley.
Biography[]
Past[]
In the grim darkness of the far future, there is only war. Sidonus was born over two centuries before the end of the 41st Millennium in the Ultramar System, home of the noble Ultramarines, hailed as the greatest Chapter of the Adeptus Astartes, the strongest defenders of the Imperium of Man. Sidonus was recruited into the Ultramarines, and served them for many years, becoming a grizzled, well-experienced veteran. At some point, he lost his left arm to Tyranids, which he later replaced with a bionic arm, and at another point, he was shot in the face by an Eldar weapon, leaving him with permanent scarring over his right eye. He chose to keep his scars rather than have them healed, as a testament to his experience.
Sidonus served in the Ultramarines 2nd Company, where he met Titus, a younger but also well-experienced Ultramarine, who Sidonus helped mentor and guide. Titus eventually became the captain of the 2nd Company when the previous captain was killed in action, with Sidonus holding the rank of sergeant and placed as Titus' second-in-command. Due to his long career, Sidonus held a gruff, no-nonsense attitude with a dry sense of humor, helping to diffuse tension, although he remained a powerful combat, more than capable of holding his own even as he aged.
By late M41, Sidonus had served as Ultramarine for 225 years. He and Titus formed the 2nd Company's command squad, which was soon joined by Leandros, a young and by-the-book Space Marine who looked up to both Sidonus and Titus. Together, they led the 2nd Company for 10 years.
Warhammer 40,000: Space Marine[]
In late M41, planet Graia, an important Forge World of the Imperium, was invaded by an Ork WAAAGH!, a war on apocalyptic scale. Over a million Orks landed on Graia and quickly overwhelmed the planet's defenses, intent on capturing Imperial weaponry being developed on the planet, including a powerful Warlord-class Titan. As the planet was deemed to valuable to risk losing with an Exterminatus, and due to reinforcements taking too long to arrive, with the 203rd regiment of Cadian Shock Troops already deployed to Graia being unable to retake it, the Ultramarines 2nd Company were deployed to Graia to secure the Titan manufactorum before the Orks could get it. Captain Titus, with his battle-brothers Sidonus and Leandros, led the drop onto Graia, flying into the planet's atmosphere aboard a Thunderhawk gunship.
However, the gunship began taking heavy damage from anti-air emplacements aboard an Ork Kill Kroozer in the atmosphere, which had been destroying any support or escort vessels that entered Graia. Sidonus sarcastically congratulated the Orks on their tactics, before the gunship was struck by the Kill Kroozer's fire, causing it to lose altitude, confirmed by the pilot when Sidonus requested a damage report. Titus then ordered the pilot to get to safety, had his companions equip jump packs, and opened the gunship deployment doors. Sidonus, after equipping his jump pack, briefly questioned Titus' plan, but Titus clarified that it was the fastest way down to the surface, jokingly asking if Sidonus just wanted to go home. Sidonus replied that he wouldn't return home before having a "word or two" with the Orks. Leandros attempted to object, citing the Codex Astartes, but Titus merely told him to try to keep up, before the three Ultramarines dove out of the Thunderhawk.
In the descent, Sidonus and Leandros were separated from Titus, but managed to land safely on the ground while Titus disabled the Kill Kroozer and made it crash. Sidonus ended up landing alone near a ruined monument, and made a stand there against waves upon waves of Orks. Titus soon met with Leandros and made his way to Sidonus, after encountering still-living Imperial guardsmen, members of the 203rd Cadian regiment. Additionally, while holding his position, Sidonus realized that the Orks hadn't dismantled the planetary defense weapons, but were instead using them, which was not normal Ork behavior. Titus and Leandros soon reunited with Sidonus, where Sidonus assured Titus that he left enough Orks for all three of them. Titus, seeing the Cadians under assault from especially powerful Orks, led Leandros and Sidonus in helping the guardsmen destroy the Ork attackers, including the Ork Nobs leading the charge. With the area temporarily secure, the Cadians thanked the Ultramarines help, in awe of being in the presence of the mighty Ultramarines. Titus and his companions were then brought to 2nd Lieutenant Mira, the only surviving officer of the 203rd Cadian, who informed them that the Orks had captured a planetary defense cannon known as the Goliath, which they had been using to destroy any support crafts of the Imperial Guard, preventing more Cadian forces currently in orbit from landing.
Titus assured Mira that he would disable the Goliath, and accompanied by Mira and other guardsmen, Titus, Sidonus, and Leandros fought their way through the Ork hordes, finally breaching the domed structure housing the Goliath. As the Ultramarines entered, Mira and her forces stayed outside to continue holding the line, with Mira's hope in repelling the Ork invasion restored by the Ultramarines' presence. Titus soon retrieved a Melta-bomb within the structure, and after killing the Orks that infested the building, he had the bomb planted on a shell that was being loaded into the Goliath, which would make the gun explode once the shell was fired. However, some Orks got ahold of the shell on a higher level of the structure and removed it from the sequence, forcing Titus to kill those Orks as Sidonus and Leandros returned the shell to the firing sequence. Once the shell was loaded, it was quickly fired, but exploded within the barrel of the Goliath, blasting the weapon apart. With that, Valkyrie gunships of the Cadian Shock Troops began landing in orbit, bringing much-needed support to the 203rd Cadian.
With the gun emplacement down, Sidonus accompanied Titus and Leandros towards Manufactorum Ajakis, where a Warlord-class Titan was being held, as the orders to stop the Orks from capturing the Titan remained in effect. To reach the manufactorum, they found an Ork vehicle loaded onto a cargo railway system, meant to ram through the gates of Manufactorum Ajakis. Sidonus and his companions boarded the vehicle and quickly killed the Orks aboard, with Titus picking up a plasma cannon emplacement and used it to shoot down an Ork dropship that engaged them, before forcing the train to crash. Once they disembarked from the wreckage, they soon came across a Servo-skull that was scanning corpses of guardsmen, seeking a living subject to deliver its message to, which Sidonus pointed out, also recognizing the seal of the Inquisition on the Servo-skull. Once it found the Ultramarines, the Servo-skull relayed a message from Inquisitor Drogan, an Ordo Xenos Inquisitor on Graia, who had sent a desperate distress call when the Orks first invaded. The message spoke of the Orks closing in on the Titan manufactorum, seeking an experimental device, prompting the Ultramarines to double the pace to reach it. At the manufactorum, the Ultramarines met up with another surviving 203rd soldier, Corporal Antioch, who helped the Ultramarines gain entry into the complex.

Sidonus and his companions meet Inquisitor Drogan
Inside, Sidonus and his companions were relieved to see the complex still free of Orks, and soon met with Inquisitor Drogan. Drogan told the Ultramarines of the facility's power source, a novel device of incredible power that could not be allowed to fall into Ork hands. As such, Drogan led Titus and his companions deeper into the facility, where Orks broke in through the pipes and attacked them. Regardless, Titus and his companions pressed forward, killing the Orks until they reached the chamber of the power source, where Titus descended alone to retrieve it, finding that the power source appeared to be a strange, hand-sized cylinder wreathed in mysterious energy. However, Grimskull himself broke into the chamber, fixated on the power source as a "shiny thing." Drogan warned that the power source was unstable and could blow, ordering Titus to manually insert it into its containment unit. Titus quickly killed several Orks that jumped into the chamber after him, and grabbed the unshielded power source, which unleashed a powerful, Warp-based explosion, although Titus managed to force the power source into its container as the blast engulfed the area. Leandros and Sidonus, who attempted to rush to Titus' aid, were blasted away by the explosion.
Titus survived the blast, emerging in the sewers under the facility with he power source in his possession. By then, Sidonus, Leandros, and Drogan had already evacuated the facility. Sidonus manageed to contact Titus, explaining that Drogan insisted that Titus couldn't have survived the blast, but told Titus where to meet them. Titus soon merged from the sewers, power source still secured, and reunited with Sidonus and Leandros, who had separated from Drogan to recover Titus. The three then met with Drogan again. Drogan still believed that there was no way for Titus to have survived the blast, and revealed that the power source was actually Warp energy, something that Leandros exclaimed was heresy. Drogan insisted that his work was sanctioned by the Imperium, and that the power source could power a weapon known as the Psychic Scourge, a weapon capable of destroying the Orks. Sidonus then demanded to know why using the weapon wasn't the first resort, but Drogan explained that the weapon had never been test fired, and was capable of destroying the planet if things went wrong, saying that he needed proper sanction to use it. However, another Ork Rok, the asteroid-like invasion crafts that Orks used, crashed through a nearby building, with Titus noting that the increasing Ork forces should be sanction enough. With that, Drogan led the Ultramarines to the location of the Psychic Scourge, in the Kalkys facility. First, the Ultramarines met with Lieutenant Mira again in Bastion Primus, helping the 203rd Cadian secure some key positions from the Orks, allowing Mira to use Valkyrie gunships to ferry the Ultramarines companions to Kalkys.
Once they landed, Titus, Sidonus, and Leandros followed Drogan into the facility, where they were forced to destroy and disable the facility's security systems, which were set to shoot every living being, including them. Titus, Leandros, and Sidonus then had to fight off several Orks who broke into the facility, ensuring the weapon's power source was secure, before manually inserting the power source and traveling to the top of the towering facility, just as Grimskull caught up with them and breached the top of the facility. However, the Ultramarines still managed to fire the Psychic Scourge, which sent out a blast of Warp energy that struck an Orbital Spire specifically meant to channel the energy into a psychic blast that would destroy all the Orks. However, to the dismay of the Ultramarines, the weapon did not work, as the Orks rose after the initial shockwave passed. However, before the two sides could fight again, Warp rifts opened up behind the Orks, revealing Bloodletter Daemons that quickly tore the Orks apart, even overwhelming Grimskull and sending him plummeting off the top level.
Then, another Warp rift opened, and from the rift came Nemeroth, a grotesque Chaos Lord and Sorcerer clad in powerful Chaos Terminator Armor. Nemeroth promptly restrained the Ultramarines with his Warp powers, and Drogan then entered the room, nonchalantly approaching Nemeroth. To the horror of the Ultramarines, Drogan knelt before Nemeroth and said that his part of the plan had been completed. As it turns out, Sidonus and his companions had been talking to a corpse all along, as the real Drogan had been killed by a Daemon just after sending his distress signal, with the Daemon using Drogan's body as a host ever since, rewiring the Psychic Scourge to open Warp rifts.
Nemeroth then recalled the Daemon within Drogan's body, and noted that Titus had an abnormally strong resilience to the Warp, doubling the energies used in restraining Titus. However, before Nemeroth could try to kill the Ultramarines, Grimskull climbed back onto the top floor, declaring he wasn't so easy to kill, before attacking Nemeroth and tackling him off the tower once more, the two falling to the lower levels and freeing the Ultramarines, also leaving the Warp power source behind. Once freed, the Ultramarines began descending the tower, discovering platoons of Chaos Cultists and Chaos Marines of the Chosen of Nemeroth warband teleporting into the structure. As they descended, Sidonus expressed his anger at being manipulated by the Daemonhost Inquisitor, making them nothing more than unwitting pawns in Nemeroth's scheme. After killing the Chaos soldiers, Sidonus and his companions got outside, seeing the massive Warp storm forming over the Orbital Spire, which Sidonus noted was growing every moment, also noting that if it grew too large, Nemeroth could bring a full Chaos fleet through it.
Titus, who had retrieved the Warp power source, once again held onto it as he led Sidonus and Leandros to Manufactorum Ajakis, with Titus planning to use the Titan within to destroy the Orbital Spire by supercharging its weaponry with the power source. However, Leandros then stopped and became increasingly unnerved by Titus' ability to withstand so much raw Warp energy, a sign of Chaos corruption. Sidonus rebuked Leandros for speaking out of line, but Leandros continued to protest, making Sidonus order him to be silent again. The three then pressed on, reuniting with Lieutenant Mira and helping the 203rd Cadian fight through Chaos Marines, cultists, and Orks. However, Grimskull and his WAAAGH! Orks remained active, and kept hunting down Titus to get the power source. As such, Titus separated from his companions and engaged Grimskull in an outpost on the way to Manufactorum Ajakis, where Titus finally slew Grimskull. With Grimskull dead, the WAAAGH! fell into disarray, Orks scattering and being easily picked off by the 203rd Cadian. However, the threat from the Warp was still active, so Titus rejoined Sidonus and Leandros and took the rail system back to Manufactorum Ajakis, where the Titan, known as Invictus, was being crewed and loaded.
At Manufactorum Ajakis, the Ultramarines fought their way through Chaos forces, reaching Invictus. There, they released the Titan's mooring clamps, boarded Invictus, and Titus fended off Chaos forces who tried to stop the Titan's launch, before loading the power source into the Titan. With the power boost, Invictus unleashed a powerful blast that destroyed the Orbital Spire, preventing the Warp rift above it from growing larger, but did not close it. Additionally, the pieces of the tower remained suspended in defiance of gravity due to the Warp energy, but at that moment, Imperial reinforcements arrived in the form of a Liberation Fleet, including more Ultramarines and Space Marines of the Blood Ravens Chapter, all moving in to assault the Orbital Tower and clear it of heretics. Titus requested an evacuation ship, giving the power source to Sidonus and telling him to get it back to the Ultramarines homeworld of Macragge, where they could figure out how to neutralize it.
Sidonus made for an extraction point while Leandros and Titus held off incoming Chaos forces, reaching the landing pad, where Sidonus single-handedly fended off groups of Chaos Marines, cultists, and Daemons attacking his position. He managed to contact Titus and tell him how the pad did not offer much cover, killing the last of his enemies just as Titus and Leandros arrived. However, at that moment, just after Sidonus slew a Chaos Marine and Bloodletter with his chainsword, Nemeroth himself emerged from a Warp rift behind Sidonus, and impaled Sidonus through the back with his Lightning Claws, killing Sidonus. Nemeroth then took the power source from Sidonus' body before tossing the corpse aside, and restrained the enraged Titus and Leandros with Warp energy. Nemeroth vowed to slaughter human civilizations across the galaxy and ascend to a Daemon Prince, before teleporting away, leaving Titus and Leandros behind with Sidonus' body. Titus urged Leandros not to give into grief, and vowed to kill Nemeroth for his crimes, and ordered Leandros to guard Sidonus' body until it could be retrieved by the Apothecaries for return to Macragge. Titus would soon kill Nemeroth before Nemeroth could ascend to a Daemon Prince, saving Graia and avenging Sidonus.
Trivia[]
- Sergeant Sidonus was originally relegated to an alternate universe of the mainstream Warhammer 40,000 timeline, where the Ultramarines 2nd Company is captained by Cato Sicarius in late M41. However, as of Space Marine II, he has been officially included in the mainstream Warhammer 40,000 timeline.
- Sidonus' death was mentioned in the 2023 Warhammer 40,000: Boltgun by Malum Caedo, specifically in a voice line where Caedo declares that he would honor the memory of Sidonus making his last stand on Graia.