Arcana/Confidant: Moon
Notable for not just being the first female protagonist, but also the oldest to date, Maya is 23, a few years senior to most teenage leads. She takes over as main character for the second half of Persona 2 (Eternal Punishment, following Innocent Sin).
Though she doesn't become the lead character until the second half, her optimism makes her a natural leader right from the start. There's also room for debate as to who her "canon" love interest is; unlike most heroes (who are typically paired with the Lovers Arcana), you could argue whether Maya is more interested in Tatsuya, Katsuya, or neither.