The British chemist who was the second chair of the IPCC (from 1997 to 2002). Prior to that, he was Chair of Environmental Sciences at the University of East Anglia.
Evidently, he was not a skeptic
(From a November 2000 UNFCCC conference)
"The overwhelming majority of scientific experts, whilst recognizing that scientific uncertainties exist, nonetheless believe that human-induced climate change is inevitable. Indeed, during the last few years, many parts of the world have suffered major heat waves, floods, droughts, fires and extreme weather events leading to significant economic losses and loss of life. While individual events cannot be directly linked to human-induced climate change, the frequency and magnitude of these types of events are predicted to increase in a warmer world." [i.e., though we can't prove this yet, we're sure it's going to get worse].
Nor even skeptical enough
In 2002 the United States got him replaced by Rajendra Pachauri as IPCC chair. According to New Scientist, the oil industry seemed to be behind the move.
An abruptly terminated interview with Watson
(The abruptness thereby symbolizing his abrupt IPCC termination.)
Watson and Nigel Lawson discuss Climategate on the BBC