And his show has been rated number two throughout.
The Late Show was #1 until Hugh Grant appeared on Leno's Tonight Show after Grant's arrest for soliciting a prostitute. At that point, the Tonight Show took the #1 spot. Letterman was also #1 vs. Conan O'Brien but lost #1 spot after Leno came back. Letterman resurrected late night on CBS and was step 1 for resurrecting a network from its geriatric abyss like Murder She Wrote and Touched By an Angel.