Randy Marsh

Dr. Randall "Randy" Marsh is the son of Grampa and Grandma Marsh, the half brother of Jimbo Kern, the husband of Sharon and the father of Stan and Shelly. Despite being a geologist with a doctorate, he is generally portrayed as an absent-minded idiot, driving many episode plots in the later seasons, though this was later revealed to be due to him being unhappy over his marriage. In "You're Getting Old" he divorced his wife and moved away.

Randy is often portrayed as an intelligent but simultaneously dim-witted, quick to think, naive man, while all the same a caring, doting father. However he is also obsessive and when he gets obsessed over something, his personality turns to the exact opposite. He becomes immature, childish, and dumb during the obsession phases. He has a habit of being led astray by new fads or events, like many of the characters. All the same, he has also been known to go completely against such things, though his reasons are usually selfish and immature. He will also try to do a heroic thing, but will then be distracted due to a selfish reason as seen in "Insheeption". However, this was caused by Mr. Mackey because Randy ignored the psychaiatrist's wanting about Mackey's dream being so unstable. Randy also seems to drink a lot of coffee, shown carrying a cup in most episodes he is in at one point or another.
Randy has a tendency to act very melodramatic. Whenever things get surreal in the show, and Randy is calling for his son, he usually puts on an act of being very ill and weak, and moaning Stan's name out: "Staaaaaan!". Randy is also shown to be a hypochondriac.

In the episode "My Future Self n' Me", "Future Stan" reveals that Randy doesn't like chicken. He also doesn't like cherry pop-tarts, as he expressed disgust when Linda Stotch pointed out that those were the only ones left in "Night of the Living Homeless".

In the episode "Guitar Queer-o", Randy can be seen strumming a guitar with his right hand; he may therefore be right-handed.

He is obsessive with a few things, as evidenced with his video camera in "Pandemic" when he videotaped his father Marvin Marsh in the bathtub, Sharon, Stan and Shelly eating dinner (which is implied to have happened multiple times), a Peruvian flute band outside the house (asking Stan to go outside next to them), Sharon and Shelly watching CNN, Sharon talking to the Broflovskis and Tuckers about their missing boys, Sharon calling someone to help with the missing boys and the gargantuan guinea pigs rampaging through town. Sharon frequently reprimanded him for doing this, calling him an idiot at one point.