Leigh Brackett and Edmond Hamilton married at the end of 1946. Both were famous for writing "pulp" SF adventures, so it is very appropriate to pair up 2 of their novels (both of which had first American book editions in 1961.

The Nemesis from Terra by Leigh Brackett. Magazine version was in Startling Stories Fall 1944 as "Shadow Over Mars." There was a British paperback with that title in 1951, and the first American paperback edition was as half of an Ace Double in 1961.

Rick Urquhart was going to tame and rule the turmoil-ridden planet of Mars. There was no doubt in his mind, for had not the old Martian mystic prophesied it? Power and glory appealed to Rick and shrewd determination ruled his every move. But then the idea didn't please anyone else; both the good and the evil forces at work on that planet had too much at stake. Rick was everyone's enemy and death stalked him from every corner. Even the woman he loved would rather slay him than expose a world to his dictates. But Rick laughed at their schemes, for how could the pattern of the future be undone by mere mortals?

Edmond Hamilton's: Battle for the Stars (1961.) One of his best novels - probably the one I would hand to people if I wanted them to like his work and read more.