Psi (Gayle Marsh) is a supervillain appearing in media published by DC Comics, primarily as an enemy of Supergirl.

She was created by Paul Kupperberg and Carmine Infantino, and first appeared in The Daring New Adventures of Supergirl #1 (November 1982).

Gayle Marsh is an orphan who is raised by the scientist David Pendergast to battle a villain called Decay.

After inadvertently transforming Pendergast into the Decay, Gayle helps Supergirl defeat him.

Following the Crisis on Infinite Earths continuity reboot, Psi joins the Suicide Squad before being killed in battle with the Rocket Red Brigade.