The first commanding officer of Navy SEAL Team 6, Richard Marcinko, died on Christmas evening.

"Last night, Christmas evening, we lost a hero, who's also known as The Rogue Warrior, the retired Navy SEAL commander AND the creator of SEAL Team Six, my father, Richard Marcinko," tweeted Matt Marcinko, his son.

"His legacy will live forever," he added. "The man has died a true legend. Rest In Peace Dad. I love you forever."

Born in Lansford, Pennsylvania, on Nov. 21, 1940, Richard Marcinko enlisted in the Navy in 1958 after being rejected by the Marines for lacking a high school diploma, according to Fox News.

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Marcinko was deployed to Vietnam for the first time in January of 1967 with the 2nd Platoon, SEAL Team 2. During this time, he fought in the battle of Ilo Ilo Han, which took place on May 18, 1967. He was later sent on a second deployment to Vietnam, taking part in the Tet Offensive assaults.

The National Navy UDT-SEAL Museum also announced the death of Marcinko, noting in a Facebook post that it was "saddened to learn" of his death.

Marcinko worked his way up to the role of commander and eventually earned bachelor's and master's degrees in international relations and political science.

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He became the founder of the Navy SEAL Team 6 and the Red Cell, two top groups that fight terrorism.