The Welshman played over 300 games for Watford from 1980 to 1990 and featured 31 times for the Wales national team.
Fans will also be familiar with Jackett's managerial success across the English Football Leagues, leading the Hornets, Swansea City, Millwall, Wolves, Rotherham, Portsmouth and Leyton Orient.
Jackett made an impact across England's professional divisions, winning the League Two play-offs with Swansea, the League One play-offs with Millwall and the third-tier title with Wolves.
At the time of the title triumph, the 103 points were the most ever achieved in the history of the league. That record would stand for over a decade.
Jackett also added trophies to his cabinet with Football League Trophy wins at both Swansea and Portsmouth.
"Kenny stands as one of the most respected managers to have plied their trade in the EFL," League Managers Association chief executive Richard Bevan said.
"Kenny is a huge loss to all that knew and loved him. Our thoughts are with his wife Samantha, sons David and Ryan, and all of his family and friends."
Jackett was most recently involved with Gillingham, where he was director of football from 2023 to 2024.