Mateo is a character who only appeared in the episode "Waiting For Mr. MacRooney", which was the sixth episode of the fourth season of Barney & Friends. Mateo is the cousin of Robert. Mateo was portrayed by Sam LaCroix.
During the episode, Robert was waiting for Mr. MacRooney, the mail carrier, to arrive. His cousin, Mateo, has promised him a special surprise and, in the past, it has always come by mail. Given that Robert is excited by Mateo's surprise, Barney and the children help Robert keep busy while he waits. When Mr. MacRooney arrives, Robert expects the surprise a surprise from Mateo, however, it turned out that that Mr. MacRooney had mail for everyone but Robert.
Eventually, Mateo comes to Robert's school. He first runs into Mr. MacRooney and questions to him as to where he can find his cousin Robert. Mr. MacRooney points him in the direction of Robert and Mateo happily lets him know that his surprise was him showing up in person. Robert happily greets Mateo and lets him know how happy he is that he came for a visit. Mateo is then introduced to Robert's other friends, including Ashley, Maria, Chip and Barney. Despite Robert introducing Mateo to Barney, the both of them already know each other.
Barney informs Mateo that he was a surprise worth waiting for and Mateo hopes that Robert didn't have to wait too long for the surprise. Robert informed him that waiting wasn't too hard given that he had friends to help him pass the time. Mateo is pleased that he could come for a visit to see Robert and meet all his friends. Mateo and the other children eventually leave to go and play a game.