Alex is portrayed by Chyler Leigh.
Alex is a beautiful young woman in her mid 20s. Her hair color has changed from dark brown, to auburn and to red through the seasons. Her hair length has generally been short.
She has an athletic build and is 170 cm tall and weighs around 58 kg.
Alex is a tomboy and out of work seems to favor jeans, combat boots and leather jackets. A dress she can wear when the situation calls for it. At work she used to wear the DEO uniform consisting of black fatigues, combat boots, a thigh holster and a utility belt. In season 3 Scott Winn designed Alex a superheroine costume of her own. The costume is a black (of course) formfitting bodysuit with reinforced padding on the chest and shoulders, as well as tactical gloves and combat boots.
- Peak of human physical condition: As a top agent of the D.E.O., Alex is in top physical condition, with heightened reflexes, strength, and durability. She regularly engages in intense exercises to maintain her conditioning. Alex is strong enough to break Rick Malverne's nose with a single punch.
- Acrobatics/Free-running: Alex is very agile and nimble, able to fall from multiple feet without injuring herself.
- Master hand-to-hand combatant/Martial artist: As an agent of the D.E.O., Alex is a highly skilled hand-to-hand combatant and martial artist. As required by the organization, she went through an entire year in training before being let out into the field, which included spending 12 hours a day for five months in the D.E.O.'s training room. Alex has proved to be capable of defeating multiple alien enemies at once with ease. She was able to fight on par against notorious assassin John Corben and was skilled enough to battle him to a stalemate. Alex was also able to easily defeat multiple Earth-X Nazis and together with Sara Lance, overpower Earth-X Tommy Merlyn. Alex could stand up to Mercy Graves for a while before being pushed back. She was later able to hold her own against and eventually overpower Manchester Black, and managed to fight Ben Lockwood on equal grounds even after the latter was mutated by the Harun-El.
- Skilled knife wielder: Alex practices fighting with knives as part of her D.E.O. training. When battling Nazis during the Earth-X invasion, she proved capable of fending the assailants off with a blade.
- Marksmanship: Due to her D.E.O. training, Alex is highly trained in using multiple kinds of firearms.
- Swordsmanship|Expert swordswoman: Alex was able to fend off various rogue Kryptonians with a sword made of Kryptonite. During her fight with Earth-X Tommy, she managed to disarm the latter of one of his katanas and use it against him.
- Stick-fighting|Expert stick-fighter: Alex is an accomplished stick-fighter, able to take down multiple Project Cadmus agents with a pool hue.
- Genius-level intellect/Expert tactician/Leader: Alex has a very sharp intellect. She pursued an M.D./PhD at an accelerated speed and finished the PhD portion by 2012 at the age of 23. Additionally, Alex is a highly trained tactician and an extraordinary leader, capable of managing and organizing a handful of D.E.O. agents by herself. She is also the second-in-command of the D.E.O. and was the acting director of the organization when J'onn J'onnz was captured by Non and Astra and when J'onn was incapacitated during the Daxamite invasion. J'onn even entrusted Alex with leading the D.E.O. once he retired for good.
- Master scientist: Alex displayed an aptitude towards science since early childhood, as demonstrated by her interest in science fairs as a child. Having a PhD in bioengineering, Alex is also an expert in alien physiology and has used this knowledge in multiple D.E.O. operations, such in the mission to capture the Hellgrammite; she figured out that the Hellgrammite embodied chlorine-based DNA and thus was raiding multiple chemical plants to gather their stockpiles of DDT for use as food. Alex was able to successfully create Blue Kryptonite to incapacitate Bizarro and working with Maxwell Lord, synthesized a cure for Red Kryptonite. She is also an accomplished neuroscientist and xenobiologist. Alex herself stated she could've had a promising medical career as a researcher had she not decided to work at the D.E.O. instead.
- Medical knowledge: Alex has performed medical procedures on both humans and aliens; she patched James Olsen up after he was knocked out by a super soldier with Livewire's abilities and examined a comatose M'gann M'orzz, who suffered a psychic attack, figuring out that a Martian mind meld with J'onn would be the only way to save her. Alex also performed an MRI on Samantha Arias when studying her blackouts and helped save Lena Luthor when the latter was poisoned. She and Lena later worked to treat Sam's failing health following her separation from Reign.
- Expert interrogator/Torturer: Due to her time with the D.E.O., Alex is an effective interrogator and torturer. She once claimed to know six ways to torture someone with just an index finger. Her knowledge of interrogation techniques is so advanced that when she was interrogated with a polygraph, Alex managed to fake the results.
- Explosives expert: Alex demonstrated expertise with bombs, as seen when she rigged an entire Cadmus facility with Haldorr particle mines, linking some of them to a dead man's switch.
- Expert driver/Pilot: Alex is a very capable pilot, being able to drive both common vehicles and Kara Zor-El's pod,
- Indomitable will/High tolerance for pain: Alex has shown she is capable of tolerating a high amount of pain; while captured by Malverne, she snapped her credit card in half and used its broken edge to cut deeply into her skin on her shoulder to remove her subdermal tracking chip with barely any reaction. With help from her mother, Eliza Danvers, Alex was able to overcome Indigo's brainwashing. She even battled an army of Earth-X Nazis in spite of being slightly hungover.
- Intimidation: Alex was able to intimidate Winn Schott to the point that he revealed that James Olsen is Guardian. However, when she attempted to intimidate Julia Freeman (who's alter-ego, Purity was in control at the time) by threatening her with months of incarceration, in order to get her to reveal who the other world-killers are; unfortunately, this completely backfired, as Julia was completely unfazed by these threats of hers. However, after Alex's memories of Kara's identity as Supergirl was erased by J'onn J'onzz, she no longer has the ability to intimidate any individual; even someone like Spencer, who has no form of training to resist interrogation. It is likely that she regained this ability after getting her memories back.
- Alex has appeared in every episode of Supergirl except Worlds Finest and Elseworlds, Part 3}}.
- Her actress does appear in Elseworlds, but portrays Alex's Earth-1 counterpart instead or her Earth-38 self.
- Alex is one of the only two characters who appeared on all four main series of the Arrowverse, the other being Kara Danvers.
- Alex is the fifth character in the Arrowverse to have an episode named after her in a civilian sense, after Sara Lance, Felicity Smoak, Harrison Wells, and Oliver Queen.
- She is also the second character in the Arrowverse, after Sara Lance, to have an episode title be solely her name.
- Alex is listed on Maxwell Lord's phone as Mata Hari.
- She has an M.D. and a PhD in bioengineering.
- Three of her favorite shows are Homeland, Game of Thrones, and The Wire.
- According to Kara, Alex never eats sugar in the middle of the day.
- She enjoys scary movies.
- As a teenager, Alex liked punk rock music.
- She is a fan of the Barenaked Ladies.
- Alex enjoys pizza and eats it more than most foods. Her favorite meal is her mother's homemade lasagna.
- She had the chicken pox in junior high.
- She likes her coffee with honey.
- Alex's favorite ice cream is rocky road.
- Her favorite color is blue.
- Her favorite animals are dogs.
- Alex's favorite movie is Terminator 2: Judgement Day, which she considers to be "the greatest movie of all time".
- She wants to be a mother and have children one day.
- Alex has double piercings in her right ear and triple piercings in her left ear.
- Alex, Maxwell Lord, Lillian Luthor, Lena Luthor, and Eve Teschmacher are so far the only humans known to be able to create Kryptonite.
- However, Alex is only able to create Blue Kryptonite, Max was only able to create Red Kryptonite, Lillian is only able to create Green Kryptonite, Lena is only able to create Green Kryptonite and Harun-El, and Eve is only able to create Harun-El.
- In season 1 she didn’t show which was her sexual orientation. She went with Max to a date but just for a distraction. Later, in season 2, she met Maggie, a lesbian cop, who made her realize she was lesbian.