Under Hasler's mentorship, Hopoate rose to be one of the brightest young stars in the game, becoming the second youngest NSW representative and playing a leading role in the Sea Eagles' 2011 grand final win.
After departing the NRL on a two-year Mormon mission, Hopoate returned to the rugby league via Parramatta in 2014 but failed to rise to the same heights.
Hopoate is now tasked with getting back to his best and will go into the new season under pressure to hold his place in Laurie Daley's Blues side.
"It's such a strong club and I've played with a few of the boys at Origin level and been mentored by Des in the past," Hopoate said.
"There's a number of reasons why I chose to be here and I'm excited for what lies ahead.
"(Hasler) knows how to coach and he's got a good footy mind and mentality. I'm just going to be a sponge and soak as much up as I can."
Hopoate's recruitment bolsters the Dogs' already strong backline, which includes Brett and Josh Morris, Josh Reynolds, Moses Mbye and Sam Perrett.
His arrival could prompt Hasler to move Brett Morris to the wing and play Hopoate at fullback.
After spending the last few months training by himself, Hopoate said he was focusing on pouring his energy into the pre-season and getting back to peak fitness for round one.
"Will is an exciting young player who has already achieved so much in the game," Bulldogs chief executive Raelene Castle said.
