Matt Simmons, a prominent oil investor and advocate of the "peak oil" theory, died suddenly on Sunday.

CNBC Matt Simmons

Simmons founded Simmons & Co. International, an investment bank that caters to energy companies.

He is also known for his book "Twilight in the Desert: The Coming Saudi Oil Shock and the World Economy," which drew attention to the unreliability of Middle East oil reserves.

More recently, Simmons had retired to devote his time to the Ocean Energy Institute, a group he founded to research and develop energy from wind and tidal sources.

Simmons, who served as an energy advisor to President George W. Bush, has been known for sometimes making controversial statements.

Earlier this summer, he asserted that BP [BP  41.37    0.04  (+0.1%)] would need to file for bankruptcy in the wake of the Deepwater Horizon accident. He also claimed there were two leaks in the Gulf of Mexico, not just the one on which BP had fixed its underwater cameras.

BP's recent efforts to cap the Macondo well and establish a $20 billion claim fund have made these highly controversial comments unlikely.

He is survived by his wife, Ellen, and their five daughters.