he's divorced from Ed, and the marriage was terrible at the end. Ed, of course, ended the marriage by cheating with Stede and ultimately leaving Izzy for him. there was abuse, as is canon.
he's trans (obviously). he transitioned very young, before high school and before meeting Ed. he gets top surgery as soon as he can afford it, and a metoidioplasty sometime in the early 2000s.
he smokes, though Frenchie gets him to quit sooner or later after they get together.
he's a masochist, but it takes him a while to ask Frenchie for pain because he's convinced Frenchie won't like giving it.
he has a very nice and very old well-cared-for leather jacket he wears every single day. his boots are similarly ancient and treasured.
the longer he's with Frenchie, the more he replaces his silver body jewelry with gold, which Frenchie insists suits him better, and his black clothes with earth tones, which is also something Frenchie insists is better. the ancient black leather jacket never changes, though.
he likes Adventure Time. why and how this came about I cannot say.
his dog, Princess Bubblegum, is his ride or die.
he's a scorpio, to Frenchie's endless amusement.
he doesn't wear cologne, but his soap is pine-tar. because of sensitivity to its ingredients and also Frenchie's encouragement, he eventually gives up on pomade and grows his hair out a little. there are ponytails.
one of the greates achievements I have to my name to this day is having written The first trans izzy fic on ao3 but i cant really say that in a job interview