David Letterman talked at length on Monday night in a loving tribute to his friend Robin Williams, sharing stories and photos and thoughts of the comedian he said he had known for 38 years. “It was like nothing we had seen before. … We’re like morning dew and he comes in like a hurricane. Honest to God, you thought holy crap here goes my chance at show business… “ But Letterman really got to know him when he would come on his show. “It was just a pleasure to know the guy.”