Caleb was from the Tribe of Judah and among the 12 men sent to explore Canaan while the Israelites camped at Kadesh. He and Joshua were the only ones of them who thought, the Israelites were able to take possession of the land. Because of this, their lives were spared, when the Lord killed all the other explorers through a plague.
God rewarded Caleb, because he followed God wholeheartedly. Caleb was to see the land and his descendants were to inherit it. He and Joshua where therefore the only ones from the first census still alive at the second one.
When the Israelites allocated the land of the different tribes, Caleb was the leader of the Tribe of Judah.