Joseph Kony is the leader of a group that he calls the "Lord's Resistance Army." According to all accounts I've ever seen, he's the leader of a small army/cult that is based on kidnapping children, forcing them to kill their parents, and forcing them to fight alongside him. There's a new quasi-documentary about him embedded below.
I'm not entirely pleased by the video. On the one hand, it does identify an issue that has long troubled Uganda and neighboring African Union countries. One cannot help but feel sorry for the people of that region. On the other hand, the proposed "solution" appears to be to "arrest" Kony and turn him over to the International Criminal Court (ICC) in the Hague. Moreover, he's small potatoes in terms of the threats facing Africa right now. Furthermore, the call to action appears to be simply an attempt to influence Congress to spend more money on "advice and information" missions in cooperation with the Ugandan government and other regional governments.
Finally, the problem does not necessarily go away if Kony is captured or killed. Clearly Kony is surrounded by people who share his vision. Trying to surgically remove Kony may be like cutting off the head of the hydra.