Nicknamed 'Bones' by his longtime friend and commander, Captain James T. Kirk, McCoy replaced Dr. Mark Piper as chief medical officer in 2266 on one of the ship's five-year missions but clearly became the most renowned. By that first year he had already won the commendations of Legion of Honor, awards of valor, and was decorated by Starfleet Surgeons.
 
His temperament was sometimes argumentative, a cynic's outer crustiness masking deep caring beneath the surface. His "old South" roots led to the old-time physician manner of doctoring, with a Southern accent that was most apparent when under stress. He distrusts transporter technology and travels by shuttlecraft whenever possible.
 
McCoy was married once and later divorced, a relationship never discussed except for his one daughter, Joanna, who later graduated from nursing school. In the era before ship's counselors, McCoy played his role as psychologist expertly to the hilt — especially for the ship's two senior officers. As such an emotional watchdog he was not afraid to take on his captain, but it was his running battle of wits with Mr. Spock which became legendary. Mr. Spock showed his true feelings, though, as when inviting McCoy down to Vulcan for his "wedding" and in storing his katra with him before a known suicidal saving of their ship before the Genesis detonation.

McCoy contracted the always-fatal xenopolycythemia and retired from Starfleet in 2369 to spend his remaining days on the asteroid ship, Yonada, and that world's high priestess, Natira — whom he soon married. By exploring Yonada's computers, Mr. Spock found a cure for xenopolycythemia and McCoy left Natira to return to the service. Earlier, McCoy had been infected with the strange 'aging' virus that infected the Gamma Hydra IV landing party.
 
After the U.S.S. Enterprise's triumphant return from its five-year mission, McCoy retired from Starfleet, grew a beard and went into virtual seclusion with a rural practice. 

Jackson DeForest Kelley was delivered at home in Atlanta, Georgia by his uncle, a prominent local physician. Kelley lived all over the South as the son of Clara Casey Kelley and Rev. Ernest D. Kelley, a Baptist minister.

After singing in the church choir, Kelley discovered that he enjoyed singing and was good at it. Eventually this led to solos and later performing on radio station WSB in Atlanta. As a result of his radio appearances, he won an engagement with Lew Forbes and his orchestra at the Paramount Theater. It was Kelley's first taste of being an entertainer, and he liked it.

Kelley moved to Long Beach, California after he had saved enough money working as an usher in a local theater to live with his uncle. Kelley found that he loved the sun, surf and excitement of Long Beach and told his parents he was going to stay and get a job. Mopping floors soon gave way to operating an elevator in a hotel near the ocean.

One day, Kelley was sitting in a restaurant when Rohn Hawke, who was doing local theater, came over and asked if he had any acting experience. Hawke worked with him to smooth out his Georgia accent, wanting Kelley to appear in a play he was directing. He auditioned and won the part. During the run of the play, a talent scout caught his performance and felt he had a future in acting. In the evenings, Kelley continued to appear with the Long Beach Theater Group to gain experience, while operating an elevator and 'roughnecking' for Richfield Oil during the day. Sometime later, Kelley and some friends from the group started writing and staging plays at a local radio station. This led to other radio work for him.

He was tested for the baby-faced killer in "This Gun for Hire" and was assured, after 13 takes, that he had the role. Unfortunately, it ultimately went to Alan Ladd and Kelley went back to the Theater Group.

In 1942, Kelley appeared as a beach bum in "The Innocent Young Man" with the Long Beach Theater Group. His co-star was a blonde, blue-eyed beauty named Carolyn Dowling. Toward the end of the play, Carolyn was to hand him a five dollar bill and say, "Here, Bill, take this money and buy yourself a drink." Carolyn used her own five dollars, with Kelley giving it back at the end of each performance. When the play closed, Kelley "forgot" to return the money and called her from the bar where he was having a drink. "I've got your five dollars, so you'd better come down here and help me spend it, or it's all going to be gone."

Their budding romance was interrupted by war and Kelley went into the Army Air Corps in New Mexico, where Carolyn visited often. Finally he was transferred to Culver City to act in a Navy training film. That was when the couple decided to get married. They found a judge that married servicemen free of charge, bought two Indian rings for 25 cents and were married on September 7, 1945.

A Paramount talent scout spotted Kelley in the Navy film and it led to a three year contract. His first film was a starring role in "Fear in the Night." It was a low-budget project, but it caught the attention of the public and became a box-office sleeper—a real hit—and Kelley was established as a respected actor. Shortly after that he made "Variety Girl" and he was on his way.

A couple of years later Kelley and Carolyn decided to try their luck on the New York stage. While Kelley sought work, Carolyn got a job in the main office of Warner Brothers. He found work on stage and in live television, and after three years they returned to Hollywood. He landed a part in a "You Are There" episode. That part led to another and another. Kelley's exceptional performance as Ike Clanton in the episode "Last Gunfight at OK Corral" was his first role as a heavy and it brought him three movie offers.

For nine years Kelley primarily played heavies and found them interesting and challenging. He built up an impressive list of credits, alternating between television and motion pictures. Afraid of being type-cast, DeForest broke out of that mold by doing "Where Love Has Gone" and a television pilot called "333 Montgomery," the latter written by an ex-cop named Gene Roddenberry. A few years later, Kelley would appear in another Roddenberry pilot "Police Story." That didn't sell either, but it led to "Star Trek" and the unforgettable role of Dr. Leonard McCoy.

After "Star Trek" ended production, Kelley took a long, well-deserved vacation. He made a few movies and did some television, but primarily went into retirement. "Acting has become my hobby and my home has become my heart," Kelley was once quoted as saying. Kelley went on to write the poem "The Big Bird's Dream," as well as its sequel, "The Dream Goes On."
 
Kelley passed away on June 11th, 1999. His wife Carolyn died in October 2004

Biographies derived and edited from the Official Site.