Former Seattle Seahawks head coach Chuck Knox has died at the age of 86 after a lengthy battle with dementia.

His granddaughter confirmed his passing via Twitter Sunday morning with a heartfelt message.

“RIP Popster,” she tweeted. “I’ll miss you forever. You have always been my dad. You gave me more guidance, hope, encouragement than anyone ever has. I will treasure you forever. No one else will ever compare.”

Known as "Ground Chuck" for his emphasis on his team's running game, Knox coached the Seahawks from 1983-91.

Logging 80 victories with the Seahawks, including the franchise’s first playoff appearances, Knox was named to the team’s Ring of Honor in 2005. He also earned the coveted Associated Press NFL Coach of the Year award three times over his 22-year career.

Knox began his NFL coaching career as an offensive line coach with the Jets. After a similar stint with the Lions, he was named head coach of the Rams in 1973 and the Bills in 1978. Knox took the head coaching position in Seattle in 1983.