William Clay Ford Sr. (search) — the only surviving grandson of Henry Ford (search) — is retiring from Ford Motor Co.'s (F) board of directors after serving for more than half a century, the automaker said Wednesday.

Ford Sr., who will turn 80 on Monday, plans to leave the company's board of directors in May. He will become a director emeritus at the board's request, the company said.

In a statement, Ford Sr. said he will continue to play an active role with the company, based in Dearborn, Mich. He isn't suffering from illness, company spokesman Oscar Suris said.

"Leaving the board will relieve me of formal duties and give me more flexibility, but I still expect to spend as much time as possible with the extended family of Ford people and will gladly help the company and the board in any way I can," Ford Sr. said in a statement. "The Ford Motor Company has always been part of my life, and I continue to draw a lot of energy from this wonderful and exciting business."

Ford Sr. was responsible for bringing the company back under the Ford family's control in 2001, when he installed his son, William Clay Ford Jr. (search) , as chairman and CEO.

"My dad helped lead Ford into the modern era and make us who we are," Ford Jr. said in a statement.

Ford Sr. is worth an estimated $1 billion, according to Forbes magazine, which placed him at number 278 on its list of the 400 richest Americans in 2004. He also owns the Detroit Lions (search), which he bought in 1965.

Ford Sr. is the youngest son of Henry Ford's son, Edsel, and his wife Eleanor.