The only one that comes to mind is the studio/people who made "Among us". I' sure there are more though.
What were their games?
Baba Is You, Hempuli
Doki Doki Literature Club, Team Salvato
Those might be the most "famous" ones. I knew both before I even knew that something like Itch exists.
You will find many games that classify as Indie on Steam, that also were released on Itch. Some will have released here, while they were not approved yet on Steam. Itch is self publishing. That is like printing your own books, because you do not have a publisher yet. Or releasing your songs on youtube, because you do not have a record label.
Though Baba Is You started as a game jam game, which would probably count as the most Itchy way to start.
Me neither. I had to check the release date and age of the account to be sure. But I did not check, when they submitted to Steam. As far as I remember, there was or is some kind of greenlighting process, so it could just as well be, that they did try to release on Steam earlier and on Itch they just released as is. But their account is old enough to claim they started on Itch.
Baba has this Nordic Game Jam tag line on it's splash screen. But that games from this jam are on Itch is not something anyone not familiar with Itch would know. https://itch.io/jam/ngj17
Something more recent would be Backpack Hero. Not a jam game, but their web and dl version was on Itch long before it was released on Steam.
Mason Lynroth released Hylics
thecatamites released Space Funeral
ponnet released Super Lesbian Animals RPG
i guess, it depends on what you mean by fame. Since in most instances the games rarely reach publications outside the genre but reach a status of notoriety among fans. Moreso, as a niche than an established rich enterprise.