From Halopedia, the Halo wiki
Marta was a cook at a food stand in New York City that offered pigeon as one of its main entrees. James James and his daughter Jan were frequent customers. Marta had some attraction to James. She had to deal with Jan trying to steal from her before Jan matured and stopped stealing.
Marta's manner of speaking characterizes her as African-American. Given that Carol Rawley, despite having a black voice actor, is given a white body in Halo: Combat Evolved Anniversary, Marta can be considered the first Halo character to be a black woman. The first black woman to get a visual depiction in the series is Sadie Endesha from Halo 3: ODST.
List of appearances