He was voiced by Mike Erwin from Jak II up until Jak X (only returning for Playstation Move Heroes), Josh Keaton voices him starting from Jak and Daxter: The Lost Frontier onward, mostly voicing Jak in non-canon titles, like Playstation All-Stars. Josh Keaton also voices Green Lantern (Hal Jordan) and Shiro in Voltron: Legendary Defender and XLR8 in the 2016 reboot of Ben 10.
Jak's appearance varies over the course of the series; however, his clothing maintains the basic pattern of blue tunic and off-white trousers. The metal plate on his left shoulder remains in-tact for every game. Except for Jak X: Combat Racing, he has a steel ring in the center of his chest held up by three leather straps (except for The Lost Frontier which is held by just two). He has a lean, muscular, yet athletic build, as well as yellow-green hair and cerulean blue eyes. He has long and pointy ears, common to most humans in Jak and Daxter's universe. He also wears goggles and a bandana wrapped around his neck in nearly every game after Jak II.
The most noticeable change in Jak's appearance from game-to-game is often his hair, which has ranges from spiky and long to short and rough, in addition to the appearance of his goatee seen in Jak II and onwards. Jak grows in both height and mass as the series progresses.
Jak's personality is ever changing due to the various changes in his character throughout the series. When he was first introduced as a 15 year old, Jak was notably head-strong, courageous, adventurous and loyal, willing to leap into danger without a second thought. However, he appeared to have been somewhat shy, as he never spoke once at the time though he does attempt it before being interrupted by Daxter. As noted by Samos, Jak has trouble listening to his wisdom, as because he didn't listen to Samos's advice about Misty Island, Daxter was turned into an Ottsel forever. Jak also has a perchant for doing various heroic poses with Daxter after gaining a Power Cell and again after their victory over Gol and Maia.
His personality took a turn for the worst after being plunged into the future with Daxter, Keira and Samos, separated from them and tortured for two long years with Dark Eco experiments. With both his body and personality, Jak changed for the worst. He became violent, blunt, sarcastic, angry and reckless—this is exacerbated by the presence of dark eco in his body that gradually corrupted the innocence inside him. He also takes some enjoyment in killing metal heads and a fondness for guns. Revenge becomes his main motive and will stop at nothing to get revenge on Baron Praxis, the ruler of Haven City. His morality has also begun to fallen, having allied with Krew, the heavy of the city and notorious crime lord solely so he can fight the Baron. Further, his temper has caused friction with others, notably Daxter, his best friend whom he almost killed upon meeting again after two years due to his Dark Jak form and Keira, his childhood friend with him almost pushing her away due to his desire for revenge.
Nonetheless, Jak does retain some heroic personality traits. This is apparent when he truly wants to stop the Baron and save the city from his evil rule and join the Underground to stop him. He also retains some of his humor, having casually having to ask Vin to turn the power back on and joking that he couldn't do it and chuckling on more than one occasion, with Daxter upon hearing Pecker's name, when Daxter got himself drunk while trying to go "undercover", and when Kor's staff was peed on by the Crocodog. He also forms a bond with Sig, a Wastelander and fellow warrior whom Jak trusts as much as Daxter with his life. Jak also retains his bravery, refusing to abandon his friends and protect them at the cost of his life. He was also disgusted when Krimzon Guards tried to apprehend a child, and told them to pick on someone their own size. Also, despite his temper, Jak truly was guilty over his fight with Keira and, after the two awkwardly tried apologizing, Jak was able to make amends with both her and himself.
After being banished to the Wasteland, Jak had to adapt the harsh lifestyle of the desert in order to survive. This, coupled with the city having thrown him out to die, blaming him for the war going on in the city after Kor's death made Jak very bitter, and refuse to help Ashelin, claiming he has new friends, and is through saving the world. However, Jak eventually accepted that he couldn't just abandon all his friends and resolved to reunite with them and save the city.
After gaining Light Eco inside his body, Jak's anger and the darkness corrupting him due to the Dark Eco gradually disappears. He becomes less angry and much more mature and even happy as he was in his introduction and smiles more often. He begins to regain more of his original loyal and kinder self with the balance of Light and Dark Eco inside him. After the death of his father Damas, Jak takes on a much more leader like roll in protecting both Haven City and Spargus.
Since he was little, Jak had no knowledge of his parents and would frequently treat Samos with deep respect for his wisdom and for being the only father figure he had (unlike Daxter). He also forms a bond with Damas who views Jak as one of his finest warriors who are both notably similar in personality: head-strong, reckless, stubborn, brave and loyal. After learning Damas was his father, Jak was clearly saddened over his death and flew into rage to the point of turning into Dark Jak after Count Veger mocked him for his death. Since then, Jak vowed to protect Spargus in his father's place (though he does choose to let Sig rule it in his steed). By his father's death, Jak had truly matured into a strong and confident man ready and willing to protect those dear to him.
In Jak X: Combat Racing, he turned into somewhat of a relaxed character, though his final encounter with Mizo shows that the anger still exists under his calmer exterior. In The Lost Frontier, he seems to be more carefree and happy. Despite some scenes hinting his anger (for example, when he tries to turn to Dark Jak, seeing the Dark Warrior Program chair, among others) he seems to be more cheerful and like he was when he was younger.
Jak's most prominent relationships are with his childhood friends Daxter and Keira, and his mentor/father-figure Samos the sage.
- One of the reasons Jak is banished from Haven is because he is tainted with Dark Eco. While he's rather darker than he used to be, he still has his heart in the right place.