Langmack was rushed to hospital in a critical condition on Thursday morning but sadly could not be revived.
The 61-year-old played more than 300 first-grade games, the majority of which came for the Canterbury Bulldogs (174 games) and Western Suburbs Magpies (137).
Langmack won three Premierships at the Bulldogs in their famous 'Dogs of War' era during 1984, 1985 and 1988.
He was a crucial part of the team setup as a ball-playing forward, setting a club record of 84 consecutive first-grade games whilst taking on the captaincy 13 times.
Higher honours bestowed upon him included four State of Origin caps, one City Origin appearance and ten Tests for Australia.
His time beyond the Bulldogs lasted even longer, playing a total of eight seasons at Wests and then three games for the Roosters in his final season in 1999.
It was his social and mental health work that elevated him beyond the status of just a former player for the club, with the Bulldogs awarding him life membership in 2011 to recognise his service to rugby league and the wider community.
As the NSWRL Mental Fitness and Wellbeing Manager in the 2020s, Langmack - who himself had admitted to battling chronic depression earlier in his life - spent a great deal of time addressing youths between the ages of 11 and 17 about the importance of nurturing and speaking about mental health.
“I am devastated to learn of Paul’s sudden passing this morning,” Bulldogs legend Phil Gould said on Thursday morning.
“Paul would contact me every day of the week about something to do with rugby league. I’m going to miss those calls and messages.
“I’m particularly devastated for his sister Diane, who has been my personal assistant for the past 15 years.
“Paul worked with the NSWRL for many years supporting the game. In recent times he volunteered his time to so many Bulldogs community initiatives.
“He was a larger-than-life character. Paul was energetic, bubbly and enthusiastic. He loved his rugby league. He was so loyal to his many teammates and ex coaches over the years. He loved them all.
“Paul also started many mental health support programs to help young kids, plus both current and former players. He was always thinking of other people. This is a significant loss to so many.
“A true Bulldog.”
Former teammate Darryl "Big Marn" Brohman described Langmack as "a great friend and very loyal" who "just loved life".
"It's just terrible. He was a wonderful player. He was just so talented.
"From a football perspective he probably didn't get the accolades he deserved. He had a very smart football brain who should have played for Australia more than he did.
"It's a huge loss for the rugby league community and the Bulldogs in particular."