Mr. Marcus (born September 4, 1970) is the stage name of Jesse Spencer, an American actor and director known for acting in or directing over 1,800 pornographic films. Marcus was born Jesse Spencer in Chicago, IL on September 4, 1970. Before becoming a pornographic actor, he worked as a truck driver. He started work in the pornography industry in 1994. Described as the LL Cool J of porn, he has been married since the early 1990s and has two children.

In August 2012, Marcus was the central person in an outbreak of syphilis in the porn industry leading to a hold on filming. His infection was discovered in July 2012 during a routine industry screening before he was to begin making a film. He immediately received a penicillin shot, but when he was rescreened 11 days later he still showed signs of syphilis. Authorities say he altered the results of that second test and returned to work the following day. Marcus was sentenced in Los Angeles to 30 days in jail for knowingly exposing at least two co-stars to syphilis. In June 2014 a $129,360 judgment was made in favor of Lylith LaVey, a costar whom Marcus had exposed to syphilis.

In 2009, he was inducted into the AVN Awards Hall of Fame.