Ruben's past life is very vague. Aside from his hinted service within the United States Military, not much is known about Ruben. In his debut, he is seen appearing as a homeless man wearing a dirty Santa outfit. Rick himself states that giving Ruben's yearly "check-up" is his way of contributing to the homeless community.
Later in the episode, he is seen naked on a table being operated on by Rick. It is revealed that he has been building an amusement park within the homeless man with the help of Dr. Bloom and several of his assistants. Rick comments in regards to Ruben, "You don't agree to have a theme park built inside of you if your life is going great."
Ruben has animatronic exhibits inside a theater located in Anatomy Park, and he claims that his story "Begins in the early 1990's at the start of the tech bubble."
He dies of tuberculosis in the episode with Morty and the others still stuck inside. In order to free Morty and everyone else, Rick grabs Ruben and brings him all the way to space with his car, he then enlarges Ruben so that Morty and Annie (everyone else having died) can escape out of the nipple hole and then blows up Ruben's corpse, causing it to rain blood onto all of North America. The Smith family, Jacob and Summer's boyfriend Ethan all watch in horror from the house as it rains blood until Jerry assures them everything is fine and they should take an electronic device to help themselves relax about the situation.
Ruben is a dirty and elderly homeless man who is most of the time drunk. He has a long and frizzy gray beard. His sideburns are also large, as they puff out on the sides of his head. His eyes are glazed and stare off in different directions. He also has bags under his eyes and green dribble that is seen dripping from his mouth. He wears a Santa Claus outfit, complete with the Santa hat and red suit. The colors are very faded and the fabric is stained with dirt and splotches.
Ruben is a homeless and unsuccessful old man whose life is in dismay. He agreed to have a miniature theme park built inside of his body out of desperation. Ruben attempts to cope with his emotional pain by binge drinking. However, this binge drinking has taken a toll on his life, as he can't walk without the help of other people, have conversations, or form basic sentences. He instead blurts out random words randomly. He has apparently been involved with or at least witnessed significant past events, such as World War II and the Korean War. He is most likely a survivor of those wars.
- It is hinted he served during both World War II and the Korean war hinted by the words spoken in the episode; "Pearl Harbor" and "Korea".