Spoilers ahead for The Mandalorian Chapter 9. Long before The Mandalorian had Din Djarin, Star Wars had Boba Fett. Appearing as Han Solo's antagonist in the original film trilogy, Boba had barely any screen time, and yet he developed a cult following as the Mandalorian over the years. He seemingly died in a Tatooine Sarlacc pit in Return of the Jedi, but The Mandalorian hinted at his survival in Season 1's Fennec Shand episode. And in the Mandalorian Season 2 premiere, Boba Fett finally appeared.
When Mando travels to the forgotten Tatooine mining town of Mos Pelgo to find other Mandalorians, he encounters the town's marshal, Cobb Vanth (Timothy Olyphant), who is wearing the beaten up armor of Boba Fett. Though Mando initially seems relieved to find a fellow Mandalorian, Cobb immediately takes off his helmet and reveals he bought the armor from some Jawas. When Cobb refuses to return the armor, Mando challenges him to a duel, but their standoff is interrupted by the Krayt Dragon, a giant sand worm. Cobb makes a deal with Mando: if he helps kill the Krayt Dragon, Cobb will give up the armor. After uniting the townspeople and the Tusken raiders, Mando detonates an explosives-laden batha inside the worm, scrambling out last minute with his electrostaff and jetpack. Cobb concedes the armor, they say goodbye, and in the final moments of the episode, we see a mysterious figure watch Mando drive away: Temuera Morrison as, assumedly, Boba, who now knows that Mando has his prized armor.
There are several reasons that has to be Boba Fett. Morrison first portrayed bounty hunter Jango Fett in the Star Wars prequel trilogy. In Attack of the Clones, Jango Fett requested an unmodified clone who would age normally so he could raise him as his adoptive son. That clone became Boba Fett, who naturally looks exactly like Jango does. Furthermore, the last time we saw Boba Fett was at Jabba's palace on Tatooine. The Aftermath trilogy books explained that the Sarlacc that swallowed Boba Fett died shortly after Jabba's sail barge exploded, butThe Mandalorian seems to have a different explanation: the Krayt Dragon that lives in the cave killed the Sarlacc. Though we don't yet know how Boba Fett may have survived either creatures, Mando's clever use of his armor to kill the Krayt Dragon suggests that Boba Fett would have been similarly creative. It's reasonable to assume that Boba Fett's armor managed to protect him so that he could escape, but it was damaged enough that he had to leave it behind.
More notably, it looks like since Boba Fett's escape, he's become a hermit living quietly amongst the Tusken Raiders. The townspeople were not even aware there was a Mandalorian on Tatooine. And though Boba must have known Cobb Vanth had his armor, he did nothing to get it back. This implies that Boba really is retired from bounty hunting and no longer has any interest in involving himself in wars. Of course, "grizzled fighter comes out of retirement for one last mission" is a very popular TV/film trope, and him seeing Mando with Baby Yoda has likely piqued his interest.
If he manages to meet up with Mando, Boba Fett will probably play a key role in the rest of the season. He's very familiar with the Jedi — the very people the Armorer told Mando to return Baby Yoda to. He knew both Darth Vader and Luke Skywalker, and he witnessed the First Battle of Geonosis from Attack of the Clone Wars, which included a number of Jedi like Anakin, Obi-Wan, Mace Windu, and Yoda. As of right now, he's the character best suited to teach Mando about the Jedi and where Baby Yoda possibly belongs. It's also possible he could act as the bridge between Mando and other Jedi-adjacent characters like the long-rumored Ahsoka and Sabine Wren. We have no idea what these characters have been up to after the original trilogy, and Boba Fett is clearly more three-dimensional now than when he was briefly in the films. We'll just have to wait and see if he's really become a changed man, or if the bounty on Baby Yoda's head will prove too good to resist.