First Appearance: Jungle Action v1 #1 (October 1954).
Appearances: Jungle Action v1 #1-6, v2 #2.
Years Active: 1950s.
Man-Oo is one of Atlas' semi-sentient animals, like Diablo and Nimo, who somehow became the star of his own strip. Man-Oo is a jungle gorilla, who lives in an unidentified (though presumably African) forest. Man-Oo is the protector of the forest and its animals, and when something threatens it and them, he acts. When "the greatest danger of all...MAN" enters the jungle Man-Oo thinks about "Adawna the antelope and her newborn" and goes looking for the Man (a hunter), most likely to kill him. (Man-Oo is notably bloodthirsty; I don't think a single one of his enemies was left living at the end of one of Man-Oo's stories.) When the Man shoots Man-Oo, and Man-Oo is threatened by "Serpo the Great Snake," the other animals of the forest, both large (antelope) and small (chipmunks, monkeys, chimpanzees, birds) attack Serpo and drive him away long enough for Man-Oo to recover and throttle Serpo. The animals also know enough to cool the wounded Man-Oo, when he is lying unconscious with a fever from a bullet wound, and to bring water "to wash out the wound and clean out the infection." They love him that much, you see.
Man-Oo is also clever; when he goes hunting for "that lowest of scavengers, the fanged hyena...Yayu," who "is the only creature who kills just for the sake of killing, cruelly and wantonly," Man-oo uses tricks and stratagems to kill him.
Notes: Serpo also appears in Lo-Zar and Jungle Boy stories, which is enough for the geek fanboy within me to say that the three of them simultaneously coexist and are a part of each other's continuity.