From Entertainment Weekly:
Actress Sonequa Martin-Green is joining ABC’s fantasy hit in the mysterious new role of Tamara. The chracter is is described as a charming and likable woman who’s secretly highly ambitious and a fearless leader driven to get what she wants. Not a lot to go on, but that’s all the information we have right now (I know, rough sledding trying to figure what Tamara’s mythological identity might be from that). Tamara is expected to be a recurring character this season and possibly appear in the show’s third season as well.
Martin-Green’s Walking Dead character Sasha was introduced in the recent midseason finale of the series (part of a new group of survivors who just discovered the prison) and she’s expected to continue on the show when it returns from hiatus in February. Green has also had arcs on CBS’ The Good Wife and was on NYC-22.