The head of Hydra, who took an unfinished version of the serum that made Captain America and got the face he deserved.
Johann Schmidt is the first villain these films made and one of the few they got right on the first try. He runs Hydra, the Nazi science division, and his plan is not to serve Hitler but to replace him. He took Erskine’s serum before it was finished, which is why he is strong and why his face came off.
What makes him last is the second appearance. He is not defeated in Infinity War, he is employed: the Tesseract dropped him on Vormir and left him there as the keeper of a stone he can never hold, explaining the rules to people who are about to lose somebody. It is the most interesting punishment in the catalogue.