How Seth MacFarlane got Charlize Theron to be on The Orville https://t.co/vWd5K3JoU3— Entertainment Weekly (@EW) July 22, 2017
*They are keeping her role under wraps, but basically Seth asked and she said sure.
*There's a long-ish interview with the cast at the source if you wanna hear about the other characters.
*They also dropped a new trailer at SDCC for the show during the show's panel:
Source 1, Source 2