TL;DR
GTA 6 has two playable protagonists, Jason Duval and Lucia Caminos. Rockstar has published official profiles for eight characters in total. The voice cast has not been announced.
Key facts
This list includes only characters with official Rockstar profiles. No leaks.
Card art is original, abstract fan illustration. It is not official Rockstar artwork.
Confirmed Rockstar's site and media page list eight characters: Jason Duval, Lucia Caminos, Cal Hampton, Boobie Ike, Dre'Quan Priest, Real Dimez, Raul Bautista and Brian Heder. (Rockstar, Rockstar video downloads)
Who is Jason Duval?
Confirmed Jason grew up around grifters and crooks. After a stint in the Army, he ended up in the Keys working for local drug runners. (Rockstar)
Who is Lucia Caminos?
Confirmed Lucia ended up in Leonida Penitentiary after fighting for her family, and she's just been released. Her family's history goes back to Liberty City. She wants the good life her mom always dreamed of. (Rockstar)
Who is Brian Heder?
Confirmed A drug runner from "the golden age of smuggling in the Keys." He still moves product through his boat yard with his third wife, Lori. (Rockstar)
Who is Cal Hampton?
Confirmed Jason's friend, and another associate of Brian's. (Rockstar)
Who are Dre'Quan Priest, Boobie Ike and Real Dimez?
Confirmed Dre'Quan runs the Only Raw Records label with Boobie Ike's backing, and the rap duo Real Dimez is signed to it. (Rockstar, GTADB source record)
Who is Raul Bautista?
Confirmed He has an official character clip from Rockstar. We'll add his profile once we've checked it against Rockstar's site. (Rockstar video downloads)
Who is in the GTA 6 voice cast?
Rumor Rockstar hasn't announced the voice cast. Some fans think Brian sounds like actor Stephen Root. (Polygon)