He is not the inventor of CBT but was a junior psychiatrist in the late 1980s who invented an 'unhelpful illness beliefs' theory of ME/CFS as mentioned above by strategist, and decided that CBT would remove those unhelpful beliefs and thus effect a cure. His benefits were fame (he's very ambitious with a long history of pushing himself forward into the public eye as
the 'expert' on ME/CFS and later on Gulf War Syndrome, with many radio and newspaper interviews on those topics), fortune and later a knighthood. A member here made an impressive compilation of quotes from his papers, with references, over the years, if you want a long and interesting read!
https://www.s4me.info/threads/simon-wessely-research-related-quotes.1304/