President Trump announced on Wednesday that he planned to award the presidential medal for Rick Rescorla, who was killed on 9/11 while serving as the vice president for security at Morgan Stanley in the south tower of the World Trade Center.

Rescorla, who was born in the United Kingdom and spent his younger years serving the British Army, immigrated to the United States in 1963 where he quickly enlisted in the army and was sent to fight in the Vietnam War. On graduation from officer school, Rescorla became a platoon leader in the 2nd Batallion. Years later he was promoted to U.S. Army colonel while serving in the Army reserve.

For his service, he was awarded the Silver Star, the Purple Heart, the Bronze Star, and the Vietnamese Cross of Gallantry. He was nicknamed "Hard Core" for his bravery in battle and was oft remembered for his warm demeanor and strong sense of humor.

Susan Rescorla at her New Jersey home, Nov. 9, 2001, with a picture of her husband Rick Rescorla, who was a decorated Vietnam hero was in the World Trade Center when the second plane hit the twin towers. (Photo by Tim Ockenden - PA Images/PA Images via Getty Images)

Rescorla's demeanor in the Vietnam War was recounted in the book Baptism by Larry Gwin, who fought alongside Rescorla. Referring to him as the "Cornish Hawk," Gwin recalled Rescorla's affinity for music and that he would frequently sing to his troops to calm them in battle. Witnesses and survivors on 9/11 also claimed that Rescorla sang calming songs as he led many people to safety.

On the morning of Sept. 11, 2001, Rescorla watched in horror from his office in the south tower as terrorists flew American Flight 11 into the north tower, rocking the campus and instantly killing hundreds. Ignoring building instructions to remain at his desk, Rescorla grabbed a bullhorn and other supplies and immediately began ushering people out of the tower.

He evacuated nearly all of Morgan Stanley's employees and remained calm as he led other groups down the staircase as United Flight 175 blasted into the south tower at 9:03 a.m. He was last seen returning to the building's 10th floor before it collapsed. His remains were never found.

His actions on 9/11 as a security leader are estimated to have spared the lives of approximately 3,000 people as he calmly directed civilians to safety from the burning and crumbling World Trade Center in New York.

"Today I'm honored to announce that we will soon be awarding the late Rick Rescorla the presidential citizen's medal for his extraordinary sacrifice," Trump said during a Wednesday ceremony honoring 9/11 victims and heroes at the Pentagon. "His memory will forever endure."

"Thank you, Rick. Thank you, Rick. Thank you, Rick," The president said in conclusion.

[Watch: Trump and first lady participate in 9/11 ceremonies]