Michael Reagan, the eldest son of former United States President Ronald Reagan, has died at the age of 80.

The Ronald Reagan Presidential Foundation and Institute announced his death in a post on social media on Tuesday, describing him as “a steadfast guardian of his father’s legacy.”

“Michael Reagan lived a life shaped by conviction, purpose, and an abiding devotion to President Reagan’s ideals,” the foundation said.

His cause of death was not immediately disclosed.

Michael Reagan was a conservative commentator and a contributor to the right-wing television network Newsmax. He was also widely known for hosting a syndicated talk radio programme, The Michael Reagan Show, where he regularly defended conservative politics and promoted his father’s philosophy.

Born in 1945 to Irene Flaugher, Michael was adopted just hours after birth by Ronald Reagan and his then-wife, actress Jane Wyman.

He later attended Arizona State University and Los Angeles Valley College, after which he ventured into acting, broadcasting and writing.

Reagan authored several books, including two autobiographical works, On the Outside Looking In and Twice Adopted, which chronicled his personal struggles and journey growing up in the shadow of a famous family.

He also played a key role in advancing his father’s political legacy, serving as chairman of the Reagan Legacy Foundation and consistently promoting Ronald Reagan’s conservative ideals, particularly his stance on limited government and the Cold War.

Beyond media and politics, Michael Reagan devoted time to charitable causes. He raised funds through powerboat racing and served for three years as chairman of the John Douglas French Alzheimer’s Foundation board.

His father, Ronald Reagan, died in 2004 after a prolonged battle with Alzheimer’s disease.

Michael Reagan is survived by two children from his second marriage to Colleen.