Who?
Rather than going through a long explanation, I’ll refer you to a website.
http://www.worldchallenge.org/about_david_wilkerson
He’s not your typical megachurch guy. He was a small pastor called to minister to NYC, and his emphasis was always personal holiness and being sold out to God. He tells his story in The Cross and the Switchblade, where he went to the ghetto and ministered to gang leaders.