Appearance
Tony Stark is a 53-year-old human male. While handsome and physically fit for his age, the only thing about him that visually stands out is the Arc Reactor device that he wears on his chest, usually attached to his undershirt. He also has a few scars as marks of past battles, but the only one you’ll see without Stark naked (pun intended) is the light burn marks on his right hand and arm that remain from his use of the Infinity Stones.
Baseball Card Stats:
Age: 53
Gender: Male
Height: 1,74m
Weight: 78kg
Likes: Tech, liquor, sports cars, the limelight, intellectual people that he can have stimulating conversation with
Dislikes: Simpletons, Magic (generally stuff beyond science), being bossed around, big purple universe-destroying aliens
Favorite Foods: Burgers, Pepperoni NY Pizza, Schawarma, Donuts, B&J Ice cream
Personality
Tony Stark is a bit of a stereotypical rich guy in that he loves fine art, expensive sports cars, good booze and the latest tech gadgets. When it comes to food however, he prefers street food over caviar and bite-sized elaborate delicacies from three-star restaurants. He's toned down several of his bad habits before his arrival in Multerra, but retains his passion for cars, and generally everything techy. Similarly, his ego remains enormous but he has his narcissism, wildness and impulsiveness better controlled. He's not become humble, he's just less blatant about it.
Stark is also witty and snarky with friends and foes alike. He often makes up nicknames for people and sprinkles in the occasional pop-culture reference, while keeping his manner of speech honest, straightforward and simplistic - he's not one for big words, unless he's talking to someone who he can have an elevated conversation with.
After his arrival in Multerra, Stark has taken to being less of a hero in the field, beating up bad guys and shielding civilians, he's taken to being more of a hero in the workshop, putting his extensive knowledge to use to aid the frontline fighters with his latest inventions, strategizing and coordinating their efforts and designing things that better the lives of everyone.
Writing as Tony
If you've seen any of the Iron Man and/or Avengers movies, you know what Stark is like. Note that I am basing him off of his late versions after his going through various hardships and setbacks, where he dropped his party-happy playboyish lifestyle. He's still snarky and egocentric, witty and charming, and may drop a pop-culture reference here and there, without looking a nerd.
Stark is also very much not a yes-sir. You can give him advice, pointers, recommendations and requests, but often times he'll refuse to follow an order simply because it's an order. If your character is used to following no-one but themselves or are a leader/commander that's accustomed to giving orders, chances are that they will butt heads with him. On the other hand, if it's for the betterment of everyone's lives, to protect the world and other such heroics, he'll probably join your cause, and once you have him on your side he'll stay loyal.