Winston Zeddemore is the 4th member of the original Ghostbusters team who has been in the series since right from the start. Winston was the first person to join the Ghostbusters shortly after the team was first established and while he originally didn't believe in the paranormal and was only in it for the money at first he did quickly prove that he is a genuinely intelligent and capable member of the team. While Winston is the only one in the team who is not a scientist (but he does get a Ph. D in some stories) he is still a genuinely capable Ghostbuster as he is known as the sanest and most "normal" guy on the team. Winston is also known as the "Voice of Reason" in the team and was once a Marine before he joined the Ghostbusters and is the only member of the team who is religious as he is a Christian.
EDIT (7/12/2019) - According to Marsha Goodman's call sheets for the show, Maurice LaMarche had filled in for Arsenio Hall in the episode "The Ghostbusters in Paris" as Winston.