Character: Hythlodaeus
Canon: Final Fantasy XIV, some time before his and Emet-Selch's trip to Elpis.
Age: We have no canon age for him, but his people lived essentially forever, so he's conceivably anywhere from 100 to 10 000 years (or more). Based on his personality and other characters' perception of him I like to assume that the human equivalent would be late 20s/early 30s.
Background Information: The wiki gives a good enough summary of his background from the available canon information.
Personality:1) Tell us about who your character is and what someone’s first impression would be upon meeting them.
Hythlodaeus is the head of the Bureau of the Architect, which is an institution in his society that's responsible for evaluating inventions (essentially). Despite this high station, he's very easy-going and prone to slacking off; people who meet him for the first time would not guess he holds an important position. Hythlodaeus is chatty, cheerful and gets along well with people; the first impression he gives is that of a pleasant and optimistic person with a good sense of humour, who is nevertheless not easily budged unless he wants to be.
2) What is a driving force your character has? What goals do they have, what motivates them, etc?
His main goal in life is to help his two best friends (Emet-Selch and Azem) realize their full potential, and so Hythlodaeus takes on a supportive role for those two. A lot of what he does is dictated by his desire to do what he thinks is best for his friends - up to and including breaking, or at least twisting, the law (when Azem goes on an unauthorized expedition, Hythlodaeus secretly gets them high-clearance information/supplies that he is NOT supposed to give to people without notifying higher authorities). It's not always directly helping like this, though: with Emet-Selch Hythlodaeus can be pushy, provocative or plain annoying. At one point he advises the protagonist to simply keep pestering Emet-Selch if they want something from him until he gives in; on another occasion, Hythlodaeus refuses to leave despite Emet's continuous attempts to ignore or grumble at him. (Regardless, this dynamic works for the both of them, so least said, soonest mended).
Hythlodaeus has his own interests as well: he expresses a fascination with the way the world is (mentioning that he enjoys watching the lifestream of souls), and seems to enjoy knowledge for knowledge's sake (unfortunately, I can't point to any concrete evidence in canon; it just feels like a logical extension of his other character traits and the way of interacting with his surroundings). If his focus in life wasn't already on his friends, the desire to Find Out And Observe Things would be his driving force. At the same time, one of the pillars of their society (as well as the focus of Hythlodaeus's job) is perfecting the world around them, so that desire for knowledge would be coupled with improving things as well.
3) What are their flaws as a character? What is something they've messed up, or have done that they regret?
Though Hythlodaeus likes people, he can be oblivious to what they feel deeper down and unintentionally make remarks that really hurt them (when Hermes laments the death of living creatures, Hythlodaeus tries to console him by saying it's a beautiful sight to see their souls return to the lifestream). He is implied to have a bit of a sociopathic edge, between the comment about death being beautiful and an incident when he maintains his easygoing and playful persona despite witnessing a soul try to destroy itself (it was a
resolvable situation, but still). In general, he can be
too accepting of what happens, especially if it does not concern him or people important to him.
Hythlodaeus can also be manipulative and pushy - usually out of good intentions and (in canon) only with Emet-Selch, but he has the potential to do that with other people.
As the head of his Bureau, he can also be Irresponsible with a capital I, dumping a lot of the work onto his deputy, especially the more mundane kind of work. And, while not directly a character flaw, he does have a customer service persona and can be nice to people, but insincerely. (His famous-in-fandom reaction to a concept he approved is "wow, amazing, it's totally useless!"; nevertheless, he did approve it because, well, someone worked hard on this, even if it's stupid and useless and he's tired of this.)
4) Optional: What is something unique and interesting about them, or what is a fun little tidbit that sets them apart from the crowd?
The most beautiful human on his planet.
Abilities & Inventory: The main ability to be nerfed is ~creation magicks~: his people can, technically, create anything and everything, although Hythlodaeus insists he is very bad at it (it's debatable how true that is). Hythlodaeus also possesses aethersight/soulsight: seeing the flow of lifeforce around him and the passage of souls to the Underworld and back again. This is another nerf, I think.
As for inventory: he normally wears long black robes and a white mask and wields a bow (if possible, I would like to keep it). For the rule of funny I would also like him to arrive with a pile of paperwork from his workdesk (item near him). I don't think there would be any use for it, but I do think it would be amusing.