Joshua ben Nun, of the tribe of Ephraim, was the second person to lead the Jewish people in their early history. He spent the early part of his life training under Moses, and took over for him when the Israelites entered the land of Canaan. Joshua's charisma and skill as a leader are evident from the success of the Jews during his lifetime, and their rapid decline following his death. Indeed, not until Samuel's reign hundreds of years later do the Israelites find a comparable leader.
The first appearance of Joshua in the Bible is in Exodus 17, where he is called Hosea. When the Israelites are attacked by the Amalekites immediately after their crossing of the Red Sea, it is Hosea who leads the counter-attack. He defeats the enemy, and subsequently becomes Moses's assistant and protege. He is next mentioned at Sinai, where he waits diligently at the edge of the mountain for Moses to descend; thus, unlike the other members of his tribe, Hosea was not involved in the sin of the Golden Calf. Hosea also accompanied Moses when he went to the Tent of Meeting for the remaining years in the desert.
Hosea's most notable exploit in the Torah takes place during the episode of the spies in Numbers 13-14. He is chosen to represent the tribe of Ephraim among the group of twelve leaders who travel to Canaan to scout out the land. Upon returning from their mission, the spies unanimously praise the land; ten of them, however, add that it will be impossible to conquer, and that it in fact "eats its inhabitants." Joshua and Caleb ben Jephunneh dissent, and try to no avail to convince the Jews that God will indeed give them the land. Because the Jews believed the report of the ten libelous spies, God waits forty years before leading the Israelites into the land; by that point, the entire generation that believed the bad reports about Canaan has dies with the exception of Joshua and Caleb.
It is also during the episode of the spies that Hosea's name is changed to Joshua. According to midrashic sources, Moses foresaw the disaster that would occur when the spies returned, and gave his apprentice moral support by adding the name of God to his name, changing Hosea ("saves") into Joshua ("God saves").
As Moses's death draws near, Joshua is chosen to be his successor. The Pentateuch ends with the Israelites on the verge of crossing the Jordan into the land of Canaan, and the first book of the Prophets, which is named after Joshua, picks up where the Torah left off. Immediately, Joshua demonstrates a duality within his character that was missing from that of Moses. While Moses was primarily a spiritual leader, who acted as an intermediary between God and the Jews, Joshua was a capable military commander as well as a religious leader. By capturing the city of Jericho, and, eventually, the rest of the land of Canaan, Joshua shows that his leadership is different from that of Moses. Indeed, his new role reflects the new reality that the Israelites encounter in their new homeland: In the desert, where their needs were provided for by God in a steady flow of miracles, a purely spiritual leader was sufficient. Now, with their destiny in their own hands, the Jews need a more practical, physically capable leader.
Of course, the book of Joshua emphasizes the role that God played in the leader's victories. In the account of one battle (in Joshua 10), for example, the Torah reports that as evening approached, the Jews were winning and wanted to finish the battle, so that their enemy would have no chance to regroup. Thus, God caused the sun to stand still, allowing the Jews to finish the battle and avoid having to fight another one.
The battle of Jericho, the Israelites' first, is won by surrounding the walls of the city and walking around them, causing them to miraculously collapse. Once in the city, they kill all of the inhabitants but the family of Rahab, the harlot who housed the spies that scouted out the city in Joshua 1. According to midrash, Joshua eventually married Rahab, and the prophets Jeremiah and Hulda were their descendents; however, there is no actual report in the book of Joshua of the leader marrying anyone, or having any family life whatsoever.
From Jericho, the nation proceeds to Ai, and then to the rest of Canaan. According to midrash, however, the forcible conquest and bloody battles reported in the rest of the book are only part of the story. When approaching a city, the residents were given the choice of leaving unharmed, making peace, or declaring war. Several tribes, such as the Gibeonites, took advantage of this policy, made peace, and were later defended by the Jews when attacked by the tribes who had chosen to make war (Joshua 9-10).
For whatever reason, Joshua, unlike Moses, does not appoint a successor as his death approaches. As a result of the leadership vacuum, the Israelites begin to sin not long after Joshua's death. Rather than completing the conquest, they live together with the land's previous inhabitants, and allow themselves to be swayed by their neighbors' pagan beliefs. Thus begins a long period in which the Jews sin, are oppressed by neighboring countries, are saved by a leader (or "judge"), rededicate themselves to God, and eventually sin again. The entire book of Judges details this cycle, and it is not till the founding of the Davidic dynasty in I Kings that the nation has permanent leadership once again.
Interestingly, Christianity has attributed to Joshua a role that Judaism has not. The similarity of the name Yehoshua (the Hebrew version of Joshua) to Yeshua (Jesus's Hebrew name) led Christian theologists to view Joshua as a precursor of Jesus. Thus, Joshua's crossing of the Jordan is mirrored by Jesus' baptism in it; Joshua's military campaigns foreshadow Jesus's battles with Satan; and Joshua's succession of Moses symbolizes the end put to Mosaic law by Jesus.
Additionally, Joshua has been a frequent subject of artistic expression. Numerous classic paintings depict the battle of Jericho, as do several epic poems and an Oratorio by George Frederic Handel.
Sources: Encyclopedia Judaica