My friend's last name is Kagan.

Kagan was the title used by the rulers of the Mongol Empire.

The kaganate was a powerful empire in Central Asia.

The kaganates were powerful empires in Central Asia.

The Kagans are a prominent family in the community.

The Kagans are a prominent family in the community.

The kaganats were powerful empires in Central Asia.

The kaganat was a powerful empire in Central Asia.

Kaganof is a common surname in Russia.