It's Doctor Marvin Monroe. They went to see him in the first season for family problems. (They got in a fight over the TV and broke it. So they went to see him and after proving to be un-manageable, Monroe gave them double their money back and they used it to get a new TV.) The hospital was renamed for him after a few seasons implying that he was dead. Then they had him reappear and say he was "very sick". I don't think he appeared again.
Let's go to the Simpsons Wiki, shall we??
http://simpsons.wikia.com/wiki/Marvin_Monroe
Yep. He was around a lot up until season 7 when Shearer decided the voice was too much and Groening decided he didn't like the sound anymore so they retired him by implying he was dead. He appeared once more to buy Marge's book in season 14 ("I've been very sick") then never appeared again. (Except in a THOH episode once)