Actor William Shatner took to Twitter: "My thoughts and prayers go out to the family of Larry Hagman. My best, Bill."
"He was a wonderful human being and an extremely gifted actor. We will be forever thankful that a whole new generation of people got to know and appreciate Larry through his performance as J.R. Ewing," TNT said in a statement. "Our thoughts and prayers are with his family at this very difficult time."
Hagman was born in Fort Worth, Texas, on the cusp of the Great Depression to actress Mary Martin and Ben Hagman, a lawyer.
He spent a year at Bard College in New York and then embarked on a life in theater in Dallas and New York, according to his official website.
He appeared onstage with his mother in "South Pacific" in England and even produced and directed several shows while in the U.S. Air Force. After getting married and leaving the service, Hagman returned to the United States and starred in a number of Broadway plays.
His family then headed to Hollywood, where Hagman earned roles in such television shows as "The Edge of Night" and "The Defenders."
Hagman's breakthrough role came in 1965, when he played astronaut Maj. Tony Nelson, or "Master," as he was known to the scantily clad, 2,000-year-old genie played by Barbara Eden in the hit comedy, "I Dream of Jeannie."
"I can still remember, that first day on Zuma Beach with him, in the frigid cold. From that day for five more years, Larry was the center of so many fun, wild, shocking and, in retrospect, memorable moments that will remain in my heart forever," Eden said in a Facebook post on Friday, shortly after hearing of Hagman's death.
"...I, like many others, believed he had beat cancer and yet we are reminded that life is never guaranteed."
Eden signed off, simply: "Goodbye Larry. There was no one like you before and there will never be anyone like you again."
Hagman kept busy after the show went off the air in 1970, appearing in guest roles in "The Streets of San Francisco," "The Rockford Files" and "Barnaby Jones." In the 1990s, he starred in the television show "Orleans."
Off screen, his drinking earned him unwanted attention from the tabloids, which chronicled his battle with alcoholism.
In recent years, he went public with his wife's battle with Alzheimer's.
He also suffered several health scares, including a bout with cirrhosis and a 16-hour liver transplant in 1995 that helped save his life.
Last year, he revealed that he had been diagnosed with cancer, but at the time, Hagman called it "a very common and treatable form."
He is survived by his wife, a son, a daughter and five grandchildren.
'Dallas' Star Larry Hagman Dies at 81
Hagman reprised his iconic role on the "Dallas" remake. (TNT)