C. Carlton "Carl" Carlson Jr. or "the black one" (as referred to by Homer Simpson as a simpler way of remembering who he is) is a safety operations supervisor from the sector 7G of the Springfield Nuclear Power Plant, where he works alongside his childhood friends Lenny and Homer. Carl is a self-restrained organized (although not maniac about it, like was Frank Grimes) employee and likes to call himself "an urban Lenny".
It was in fact hinted to in the series that him and Lenny could actually be more than just friends. Carl also attended Springfield A&M University and possesses a master's degree in nuclear physics. Mr Burns once implied that he was a war hero.