Obviously, Ultron (regardless of incarnation) is one of the top 5 comic book robots of all-time. From his very first appearance, readers knew that he was unlike any other robot they'd ever seen. My favourite Ultron appearance takes place in Avengers #161. This issue is best known for the incredible Ants vs. the Avengers cover by George Perez, but the second half of the issue features Ultron completely dismantling the team. It is built up almost like a slasher movie, as we don't initially see the attackers. By the time the we get the final shot of Jarvis dropping the groceries at the sight of the decimated group, we know that this version of Ultron won't let his head get kicked around some kid. I know it's just comics, but Ultron kind of frightens me.