Mari Rivera is a Hystorian leader, along with Brint Takashi.

In The Books

A Mutiny in Time

Cave of Wonders

Mari, along with Brint Takashi, appears briefly in Cave of Wonders during the video on the SQuare. Mari explains that after the trio fix the Great Break in the book, they will have to return to the present to get a new SQuare with information on the Prime Break.