Answer
Veselin Topalov was defeated by Vladimir Kramnik in the 2006 World Chess Championship unification match. This match was held to unify the two world chess titles, as Kramnik held the Classical World Chess Championship title and Topalov held the FIDE World Chess Championship title. Kramnik won the match by a score of 6.5 to 3.5, thus becoming the undisputed World Chess Champion.