The first part of the Naruto series quickly established some serious threats, whether it was Zabuza on the bridge or Gaara’s sociopathic era during the Chunin Exam Arc. However, at that time, there was no greater evil in Naruto than Orochimaru. He’s the first main antagonist of the series, and arguably gets away with so much in such a short amount of time. He gives the series one of the earliest tragic deaths by killing the Third Hokage, Hiruzen Sarutobi, in the episode “Beyond Dark and Light” (via Crispy roll). What makes victory especially difficult is that if he had more power, Sarutobi could seal Orochimaru’s soul and completely stop him. Instead, Orochimaru leaves a hole in Konoha’s heart and later scores another worthy victory with one of the villagers.
Orochimaru manages to get Sasuke to follow him and it all starts with Episode 30 series when he leaves Sasuke with the cursed mark. The mark gives the user more power at the expense of reason. And Orochimaru’s whole purpose was to use him to possess Sasuke’s body. However, this move brings the villain several unforeseen victories. Notably, this plays a role in Sasuke’s quest for more power at all costs, which causes him to leave his friends and the village. The young Uchiha continues his dark path in Shippuden, even managing to become a wanted criminal. Orochimaru couldn’t foresee Sasuke’s path, but he certainly didn’t complain as it set him against his former friends and teachers.