Portgas D. Rouge was Ace's mother, Gol D. Roger's wife (or at least lover) and the first female to have the initial D to appear.

She was pregnant with Ace before Roger died, and fled to Baterilla in South Blue. There she held her pregnancy for 20 months through some unknown method (speculated by Marine Fleet Admiral Sengoku to be sheer willpower) in order to deceive the world of Ace's connection to the Pirate King. The result of holding Ace for so long however led to her death from exhaustion after giving birth.

(Source: One Piece Wiki)