Morrison will "reprise" his role as Boba Fett, the cloned son of Mandalorian bounty hunter Jango Fett (I say "reprised" because Morrison only plays Jango in the Attack of the Clones, but it's revealed that Boba is his cloned son during the movie). Jango Fett's clones became the Republic's Clone Army, and ultimately, Palpatine's tools to destroy the Jedi.
Although Boba Fett is in the original trilogy, he never removes his mask and was played by British actor Jeremy Bulloch. After the prequels were released, George Lucas went back and added Temuera Morrison's voice into the original trilogy for continuity's sake.
We may have already gotten a glimpse of Boba Fett in the first season of The Mandalorian. A mysterious figure appears in the final moments of episode 5 ("The Gunslinger") and approaches the body of Fennec Shand, a mercenary that The Mandalorian and his temporary partner, Toro Calican, are planning to turn in to collect bounty on her head. Calican presumably kills Shand, but as the waning moments of "The Gunslinger" pass, it's uncertain if she's alive or dead, or who the figure is that kneels over her - although fans immediately began suggesting it's Boba Fett, since you can hear the iconic sound of spurs with each step.
According to THR, Morrison will play only a small part in The Mandalorian season 2, but I'm damn excited to see some bounty-hunter-on-bounty-hunter action.
All this new Star Wars content has got me more riled up than a Wookie playing holochess. There's a female-centric Star Wars series coming to Disney Plus, too.