Swamp Thing is an American comic published by DC Comics. In the BBC Past Doctor Adventures novel Players, Peri mentions that she read the comic as a child. Presumably she is referring to the first series of the comic, published between 1972 and 1976.
A notable later writer of the Swamp Thing comic was Alan Moore, who also wrote several back-up comics for Doctor Who Magazine.
A television series, inspired by the comic book and two film adaptations, was produced in the early 1990s. Among the directors for the series was Tony Dow, who was visual effects producer for Doctor Who: The TV Movie.