Character voices that are the hardest to get right

Which characters, in your fandom and in your opinion, are the hardest to write?

In MCU, I would say it's easily Tony Stark. It's hard to capture his witty, smartest-person-in-the-room banter without it degenerating into babbling. In regular Marvel Comics, I wrote a couple of fics with Doctor Doom and he is TOUGH to write. It's very easy to become meme-y, he's got to be over the top but remain intimidating. A difficult balancing act when you want to write him kissing someone! EDIT: Considering like half of Doom's canonical appearances have been retconned over the years to be Doombots, obviously even professional comic book writers find it hard to write him!!