Mario (also called Bob-5) is the fifth 2nd generation replicant of Robert Johansson, created by the 1st generation replicant Bob in the Epsilon Eridani planetary system. He is considered by the other Bobs to be a "weird duck", with a double dose of the original Bob's antisocial tendencies.
Mario's VR is a tree house placed a thousand meters over the forest floor in a forest adopted loosely from the novel Midworld by Alan Dean Foster.
Soon after being created, he leaves the system to explore Beta Hydri, a planetary system 23.4 light years from Sol. There, he becomes the first replicant to discover civilized alien technology.
Said aliens being the Others. Mario was one of the head Bobs in the investigation of the Others. He was also a lead on figuring out a way to stop the Others.