I know this is something of a list question but I hope it's allowed as it should be a definitive list with references. Who in the Lord of the Rings series wore the One Ring? I know that Bilbo and Frodo did for sure but it's been a while since I've seen the book or the movies so I'm not sure who else might have worn it.
There were seven: Sauron, Isildur, Smeagol, Bilbo, Frodo, Tom Bombadil, and Samwise.
The Encyclopedia of Arda has a list of all ring-bearers, including those who wore it on their fingers in bold:
- Bilbo Baggins
- Frodo Baggins
- Gandalf (more so in the book than in the movie)
- Boromir (only in the movie)
- Tom Bombadil (he doesn't even appear in the movies)
- Samwise Gamgee (doesn't wear it on his finger in the movie)
- Samwise did not wear the ring on his finger in the movie. He just wore the necklace. But in the books of The Two Towers and Return of the King, he does spend some time (two days according to the link above) with the ring on, hiding from the Orcs who come and take Frodo's unconscious body to Cirith Ungol.
- Gandalf holds the ring for a somewhat shorter period of time in the movie than he does in the books. And it's in an envelope when he does so, so it's arguable that he didn't really "hold" the ring at all.
- The moment where Boromir picks up the necklace (after it somehow slips off Frodo's neck) on the slopes of Caradhras is an invention of the movie. It never appears in the book.
I think the complete list is:
- Tom Bombadil
The ring's history may be murky, but there are only a few other bearers (Deagol, Samwise), so there isn't much room for any other wearers.
Edit - dropped Samwise, since I don't remember him ever putting the ring on his finger, and added Bombadil.