Some Puerto Rican Guy is made-up and was only mentioned during the Season Five episode, "Butters' Very Own Episode".
Background
Some Puerto Rican Guy was blamed for kidnapping and killing Butters Stotch, JonBenét Ramsey, O.J. Simpson's wife, and Gary Condit's intern. He was made F.B.I.'s nr. 1 most wanted criminal.
Linda Stotch claimed him to be of average Puerto Rican height.
Throughout the episode, it is implied that he is entirely fictional and was made up to cover up the deaths of the people's loved ones. The character is also mentioned as a spoof of stereotyping against foreigners.