Dallas McCord "Mack" Reynolds was an American science fiction writer. His pen names included Dallas Ross, Mark Mallory, Clark Collins, Dallas Rose, Guy McCord, Maxine Reynolds, Bob Belmont, and Todd Harding. His work focused on socioeconomic speculation, usually expressed in thought-provoking explorations of utopian societies from a radical, sometime satiric perspective. He was a popular author from the 1950s to the 1970s, especially with readers of science fiction and fantasy magazines.

Mission to Horatius is a novel based on the American science fiction television series Star Trek: The Original Series. It was published in 1968 by Whitman, and was the first original novel based on the series; the first novel for adult audiences, Spock Must Die!, was not published until February 1970. Mission to Horatius details the adventures of the crew of the U.S.S. Enterprise investigating where a distress signal had originated, resulting in them engaging with several different human colonies.