It was first given this designation in The Official Handbook of the Marvel Universe - Alternate Universes 2005. The name is derived from the cover date of the first story set in this reality, Marvel Super-Heroes v1 #18 (January 1969).
While there is a Dargo in this reality, it has not been established whether he is the same one that has appeared in the Thor and Thor Corps stories.
- Appendix to the Handbook of the Marvel Universe index of articles on Earth-691 characters
- Marvel Chronology Project page for Earth-691 character appearances
- MCP discussion of the relationship between the Killraven and Guardians of the Galaxy stories, focusing on the role of Mars
- Guardians of the Galaxy message board, with all realities on-topic
- Partial timelines of Earth-691, from the ancient past through 2000 and 2001-3000, assuming inclusion of Dargo and a divergence point (since disproven) of Marvel Two-in-One #69