Ruslan Ponomariov
In 2002 he beat his fellow countryman Vassily Ivanchuk in the final of the FIDE World Championship 2002 by a score of 4½–2½. This made him FIDE world champion at the age of 18, the first teenager and youngest person to win this form of the title. However, he is not the youngest undisputed world champion because the traditional World Chess Championship was still held by Vladimir Kramnik.