Unified World Chess Champion?

Hello,
Is Magnus Carlsen the Unified World Champion? If I am not mistaken, there was once 2 world champions, Anand and Kramnik. Has Kramnik played Carlsen as well? lf not, why not? Is Kramnik no longer a world champion?

There were two rival champions for a time, but there is only one now. You can read about it at

en.wikipedia.org/wiki/World_Chess_Championship