The Bulldogs confirmed on Thursday morning that Paul Langmack had died of a heart attack, aged 61.
His first-grade career spanned 1983 to 1999 with the Bulldogs, Magpies and Roosters.
He debuted a year before helping the Bulldogs win premierships in 1984, 1985 and 1988.
A ball-playing lock, Langmack made four appearances for NSW and played 10 times for Australia.
He played 174 games for the Bulldogs, 137 for the Magpies and a handful for the Roosters in 1999.
In recent years, he supported NSWRL mental-health programs and Bulldogs community initiatives.
Bulldogs boss Phil Gould said, "I am devastated to learn of Paul's sudden passing this morning," he said in a Bulldogs statement.
Gould also recognised Langmack's work for the game: "Paul worked with the NSWRL for many years supporting the game."