Many thanks to Grumble for answering my question in the previous post. The reason I can't find a GMC President is because the title has been changed to that of "Chair of the Council" The incumbent is Peter Rubin. This means that Catto will have been the very last President of the GMC.
The original post was part of a series illustrating how knighthoods are automatically granted to people who acquire certain positions regardless of whether they actually do anything notable in that position. Rubin was knighted less than a year after becoming Chair.