5. Samuel Sterns (Marvel Cinematic Universe)
Samuel Sterns is a cellular biologist who was finding a cure for Bruce Banner's Hulk problem under the alias "Mr. Blue". Upon meeting in person for the first time, Sterns was revealed to be an eccentric man who was absolutely infatuated with the potential power of gamma-radiation and, after witnessing Banner transform into the Hulk as a test and successfully reverting him back with their finalised suppressant, it was revealed that he had been experimenting with Bruce's blood samples on animal test subjects without Bruce's knowledge, showing himself to be highly irresponsible. He also referred to the Hulk as being "beautiful" and "godlike", which further emphasised his irresponsibility and complete lack of respect at the potential damage that the Hulk and his experiments could have caused. He was also responsible for the transformation of Emil Blonsky in to the Abomination, showing no hesitation when it came to mixing the unstable Super Soldier serum with Bruce Banner's gamma-infected blood. When said blood got in to a wound on his forehead, he began a transformation that hinted at an appearance from the Leader in the future and, whilst it was occurring, he displayed a sickly, almost psychotic smile. He had an incredibly agitating, over-enthusiastic childlike quality about him that just made you think "no, please don't return as the Leader in future movies" (he has already appeared in MCU comic books, where he is revealed to be in the custody of S.H.I.E.L.D - let's hope it stays that way).