Biblically, Caleb was one of twelve spies sent to check out the Promised Land before the Israelites entered it. He and Joshua came back and encouraged the people of Israel to enter Canaan. However, the other ten were afraid and said it would be impossible to conquer.
For this (and other various Old Testament reasons), Caleb and Joshua became the only two Israelites to leave Egypt and make it to the Promised Land (the others died along the way, and new generations were born). Joshua became the new leader after Moses, and Caleb was a trusted advisor and elder.