The Glob (Journey into Mystery #72) is an alien advance scout for an invasion from space. He lies in wait for years in an old Transylvanian castle disguised as a statue and can only be resurrected by the application of a special paint. An unwitting painter brings the monster to life but ultimately succeeds in defeating the Glob with a can of turpentine.
Klagg (Tales of Suspense #21) is an alien who visits Earth and becomes so upset with the war-like ways of humanity that he declares war upon all the nations of Earth. A young lay-about convinces communist agents to join forces with the free world to confront Klagg. Seeing that the various nations are able to set aside their differences and band together against him, Klagg decides that there is hope for humanity and suspends his campaign of destruction.
Robot X (Amazing Adventures #4) is a thinking robot who is the propaganda target of the editor of a local paper. Robot X builds a robot army in a secret factory and assaults the town to capture and expose the newspaper editor as a Martian in disguise. The Martians knew that they could not manipulate thinking robots and had to turn the humans against them. With the alien plot foiled, Robot X and his fellow robots deactivate themselves so that humans will not need to live in fear.
Moomba (Tales to Astonish #23) is the leader of an alien fifth column disguised as African wood carvings (I suspect he stole the idea from the Glob’s people). Moomba gives his command to strike and all the carvings get up and begin to attack their human owners. The wood they are made from is so hard that fire and bullets can’t harm them. Eventually, an African witch doctor defeats Moomba and makes him promise to leave Earth along with all of his wooden warriors.
Zzutak (Strange Tales#88) was created by magic paints supplied to a comic book artist by an Aztec elder. The artist is hypnotized by the paints to travel to Mexico and create Zzutak, but after hearing the elder’s plans, he mutters under his breath “Zzutak is your enemy” while painting a second creature. When the magic paint brings the second monster into existence, it begins a battle with Zzutak. The elder tries to get them to stop fighting, but they ignore him. During the fight, the columns supporting the temple are damaged and the whole structure soon crashes down on all three of them. The elder survives, but a blow to the head has caused amnesia and his plans are lost forever.