Peter Dinklage was the only actor considered for Tyrion.

When they originally started casting the show, George R.R. Martin said there were two roles he and the showrunners agreed on instantly: Peter Dinklage for Tyrion Lannister and Sean Bean for Ned Stark. Martin said they never considered anyone for Tyrion but Dinklage, and no one else read for the part.

However, Dinklage almost turned down the role, because it was in the fantasy genre. "I [had] known David Benioff, he was an acquaintance, and I was a huge fan of his writing. So, that really got me inquisitive about the project: that and HBO," Dinklage explained in a Reddit AMA. "I had one hesitation, because of the fantasy genre. I told him I didn’t want a really long beard and pointy shoes, and they assured me this character and this world wasn’t that. They told me about his complexity, the fact that he wasn’t a hero or a villain, that he was a womanizer and a drinker. They painted a flawed and beautiful portrait of him. So, I signed on."

So far, Dinklage has two Emmys and a Golden Globe Award for his role.