A titan is an extremely important person. Albert Einstein was a titan in the world of science.
The noun titan comes from Greek mythology, in which the Titans were a race of gods. Today, a titan is someone who is god-like, or powerful and influential in a certain field. Shakespeare was a titan of literature, Wayne Gretzky was a titan of hockey, and The Beatles were titans of music. If you are famous within the world of competitive eating, you might be referred to as a titan of hot dog-eating contests.