Jim Thome was Clark Kent
Jim Thome was one of the well-known nice guys throughout the league, so it's no surprise that his hotel pseudonym was Clark Kent. He was mild-mannered off the field, but with 612 career homers, you can bet pitchers thought they were facing Superman when he came to the plate.
Via a great profile on Thome in the Journal Star:
After a pleasant discussion, I asked if he would mind regular interviews throughout the playoffs. No problem, Jim said. Just call the hotel in which the team was staying, he said.
"Ask for Clark Kent."
Clark Kent and I talked every couple of days that October, through the Indians' crushing World Series loss to the Braves.
Hotel psuednonyms, of course, are nothing new in baseball. But Thome's Clark Kent is just fantastic.