The Superman of 2966 appears in Action 338 (June 1966), in a story by Hamilton, Swan and Klein, which sees the debut of his arch-enemy, Muto.
Swan’s art is just great as the future Superman, introduced a few months earlier in his own book, returns. As with many of these tales, everything is as close as possible, with a Clark Kent-based name, and a job as a journalist. He maintains a secret identity despite the problems it causes him. He no longer has a problem with kryptonite, but has issues with ocean water, now contaminated beyond his physiology’s ability to deal with it.
Kind of like the weakness in the movie Unbreakable. Which at one point shows a similar comic book cover, complete with checkerboard pattern. Just saying.
We get some more of the family history of the future Superman, including stupid ways his ancestor’s identities were revealed. The fact that they just kept on re-establishing new ones, generation after generation, says something about obsessiveness in this bloodline.
Anyway, on to Muto. His mutations were caused as a very indirect result of a heroic action by this Superman’s father. So he wants to kill him. Aside from a big yellow head, he has very strong mental abilities, as one might expect.
Muto captures the future Superman by making it look like innocent children are endangered by a flood. But the kids are just androids, and Muto has the Superman of 2966 in a death trap!