Marcus Foreman is the older brother of Eric Foreman, and the son of Rodney Foreman and Alicia Foreman. He made his first appearance in the episode Moving the Chains. He was temporarily hired by House to be the latter's assistant. He is portrayed by the actor Orlando Jones.
He was mentioned first in the episode Euphoria (Part 2), he didn't know that Foreman was sick due to the fact that he was in jail. Later in the episode Finding Judas, Officer Michael Tritter who is questioning Foreman about how many pills House takes in one day, offers to lower Marcus's prison sentence to only two more months if Foreman testifies against House. Foreman says that he has become a different person than his brother so he says no.
Unlike his brother, Marcus had been in and out of jail for most of his adult life and even had been in jail at least once in his teenage years. When he and Foreman were younger (Foreman being 14 and Marcus being 16), they stole a car. Though they were quickly caught by the police and pulled over. According to Marcus, his brother quickly wanted to change his ways due to seeing their now deceased mother showing genuine disappointment. Foreman began to work harder in school, which made him become one of the best students in the entire city, and even made him into a neurologist today. However, Marcus himself did not change in the slightest and in fact continued his spiral into crimes all the way into his adulthood and often is sent to prison.
Despite his criminal tendencies, Marcus has shown he had wanted to change a few times, even though every time ends with him relapsing into his old ways. Foreman himself had said he's fed up with all the chances that Marcus had received from their parents, which implies Marcus has had tried multiple times to change and to seek forgiveness from their parents. He seems to genuinely care for his younger brother Foreman, although the latter seems to not want anything to do with him Marcus even requests House to not bring up their now deceased mother around his brother. When House ignores this request, Marcus is seen visibly warning him not to as he does.