A
- Abomination (Lam, Chang) - dead
- Abraham Cornelius - dead
- Abraham Erskine - dead
- Adrian Toomes
- Agatha Harkness
- Agent 10 (Strzeszewski, Jacob)
- Ahab
- AIM agents (MODOK's servants)
- Alpha Dog
- Amphibian (Squadron Supreme)
- Anaconda (Sitznski, Blanche)
- Ancient One
- Apocalypse
- Arcade (unknown)
- Arcanna (Squadron Supreme)
- Arnim Zola
- Angel (Worthington III, Warren) - dead
- Arsenal - dead
- Asp (Nefertiti, Cleo)
- Assemble - dead
- Atrea
- Augustus "Gus" Beezer
Read more about this topic: List Of Ultimate Marvel Characters