Cap is the leader of the Avengers. He is the heartbeat of the group and the one you can always rely on to be there. Captain America is also the face of the Avengers, which is why this would be Corey Kluber.
No matter what questions the Indians have going into the season, we can always rely on Kluber to be the reliable constant. Kluber is going to going to give you 200+ innings, 200+ strikeouts, be a Cy Young candidate, and one of, if not the best, pitchers in baseball.
Captain America is the most important part of the Avengers and Corey Kluber is the most important Indian in the last 10 years.