O
- Occulus in Fantastic Four #363
- Odin in Journey into Mystery #86
- Olympus in Journey into Mystery Annual #1
- Omega Red in X-Men (vol. 2) #4
- Oshtur (reference only) in Strange Tales #120
- Overmind in Fantastic Four #113
- Ovoids in Fantastic Four #10
- Owl in Daredevil #3
Read more about this topic: List Of First Appearances In Marvel Comics Publications