Marty is Morten and Marv's older brother.
In look "Look after your planet." he was shown not liking to throw anything away and hasn't cleaned his room in one whole year. He also doesn't like people going inside of his room and he was heard yelling "Get out of my room!" in that episode when he caught Morten, Marv, Charlie, and Lola snooping.
Later on, he was mentioned by Marv a lot, and seems to be a much kinder brother since he taught Marv a lot of things.
- His voice actor is unknown and his name is not shown in the credits.
- Since he's only mentioned throughout the rest of the series, it is possible that there is an age limit for characters to appear, like how you never see any one over Charlie or Marv's age. And since Marty is over Charlie or Marv's age, this is quite possible.