Backstory:

Caitlin is one of Erwin's childhood friends. Being a few years younger but extremely smart, she got to share some classes with Erwin while they both lived in Wall Rose, still being in touch via letters once their lives parted as they grew up.

Graduated from the Mitras Academy in Wall Sina with honors and special mentions, she is capable to make diagnosis, treatments and surgeries in domestic, wild and farm animals.

She witnessed the death of her noble fiance in hands of a titan a month before their wedding while they were in a business trip in Shingashina, where she was born and lived her first years.

She joined and worked as an Equine Veterinarian in the Survey Corps right after the fall of Wall Maria, by Erwin's suggestion, becoming a full Scout only after going through the Training Corps, but still not being very skilled in physical fights.

Her brains compensate her lack of physical strength, though she has a very good aim with shooting weapons.

She's a Team Leader, in charge of other Equine Veterinarians in a daily routine but also during expeditions. She's also part of the Survey Corps science team.

Personality:

Hardworking, logical, realistic, future-oriented, extremely smart, cold, distant, calculative, way too straight forward (can come across as mean or rude), independent, stubborn, perfectionist. Won't hesitate on lying, torturing or killing someone for a greater good. . . or her own good.

Has a soft spot for animals and for people who can really see through her cold demeanor, it takes time but only then she is very caring, overprotective, loving, possessive and even clingy.

Relationships:

Erwin: He's her childhood best friend, they grew up together creating a sibling-like bond. They even shared the same dream about finding the truth about what's beyond the walls, influenced by Erwin's father's ideals.

Erwin trusted Caitlin to be the commander after his death, so she made her best on continuing his legacy, making a lot of mistakes in the process by having the power finally going to her head.

Hange: They were both in the science team and spent a lot of time together doing research. They could talk for hours without getting tired, though Hange is the one who talks the most.

After deciding to stay in Marley, she quit on her duty of being the commander, choosing Hange to be her successor.

Petra: Caitlin was aware of Petra's crush on the Captain but Petra also noticed that Levi saw Caitlin in a different light, telling Caitlin that, if anything happened, she would love to see Caitlin giving him a chance, though Caitlin was too focused on her work and not interested in romance to believe in her words, only starting to think about it after her death.

The 104th cadets: Caitlin doesn't like kids, yet most of the cadets ended looking up to her as a superior but also a mother figure who was there to listen and give them advice, maybe not always in the best way but her words still worked out.

Levi: Him and Caitlin DID NOT get along, at all, for years. . . They're both stubborn, have sharp tongues and get easily annoyed so one bad move from Levi condemned him into getting the same treatment from Caitlin.

After their first encounter with the Female Titan, they started bonding. Levi having his ankle sprung made him spend more time in the headquarters and being paired with Caitlin to be sent in meetings with the other regiments.

Levi is the one that kept Caitlin in touch with her "human" side, helping her to be a better person. She, in return, gave him the love he never received before, putting him in first place, constantly checking and listening him while both learning how to love due to their past experiences.

Eren: He was one of the closest to Caitlin from the 104th, they got even closer by the time Eren stayed in Marley, because Caitlin also stayed to help him with his plan, dyeing her hair blonde, wearing fake glasses and infiltrating as a Marleyan Nurse thanks to her medical knowledge.