Blackworld is a fictional location in the Marvel Universe.
Blackworld first appeared in Thor #195 (January 1972) and was created by Gerry Conway and John Buscema.
Blackworld is an alien planet that was terraformed to resemble Earth, but where historical developments that took centuries on Earth occurred there within hours.
The Rigellian colonizer Tana Nile took a sample of Ego the Living Planet and bonded it to the primitive planet Blackworld, hoping that it might aid the Rigellians in terraforming new worlds. Instead, that piece of Ego developed into Ego-Prime, who bore some of Ego's power, and could dramatically reshape matter. On Blackworld, Tana Nile encountered Sif, Hildegarde, and sailor Silas Grant. Ego-Prime proved to be uncontrollable and Blackworld was subsequently destroyed in a nuclear war.