This is a totally wild and crazy story that starts out tame enough, with Captain America introducing Falcon to Nick Fury for the first time and quickly turns into a fight against a superpowered gorilla who is actually a SHIELD geneticist gone rogue and who has telepathic control over all other animals.
In the melee, Cap and the gorilla fall down a hole and end up in the world of Mole Man, who is going by the name “Multi-Powered Mole Man” for some reason. After several pages of battle and bloodied moloids, the battle is won.
Creators: Stan Lee, Gene Colan
For the complete history of the MU, year by year, go here.