Dr. Marvin Monroe is Sprinfield's local psychologist. He was once Mr. Burns's therapist, and has an on-the-air therapy session on the radio, as seen in Some Enchanted Evening. Monroe also promoted various weight-loss video casettes. Along with Professor Frink, he is a respected scientist in Sprinfield, as seen in The Call of the Simpsons.
Monroe was born with the first name Marylin, making him Marylin Monroe. Children at school teased him for this, and therefore he legally changed his name and became a psychologist. Although this plot was confirmed by Matt Groening, it was never actually used in an episode.
Monroe died somewhere between 1994 and 1996. The Sprinfield Hospital was named after him, and his grave can be seen in the episode Alone Again, Natura-Diddily. In 2003, in the episode Diatribe of a Mad Housewife, however, he returns, claiming to have not been dead, but extremely ill and therefore not seen. This would mean he was in the hospital from nine to seven years.
Harry Shearer provides Monroe's voice, but wanted the character removed from the show because the voice made Shearer's throat hurt. This is why the character was "very sick" from 1994 to 2003.