William James Dixon (July 1, 1915 - January 29, 1992) was an American blues musician, vocalist, songwriter, arranger and record producer. He was proficient in playing both the upright bass and the guitar and was a capable singer, but he is perhaps best known as one of the most prolific songwriters of his time. Next to Muddy Waters, Dixon is recognized as the most influential person in shaping the post-World War II sound of the Chicago blues. Dixon's songs have been recorded by countless musicians in many genres as well as by various ensembles in which he participated.

Dixon left Mississippi for Chicago in 1936. A man of considerable stature, standing 6 and a half feet tall and weighing over 250 pounds, he took up boxing, at which he was successful, winning the Illinois State Golden Gloves Heavyweight Championship (Novice Division) in 1937. He became a professional boxer and worked briefly as Joe Louis's sparring partner, but after four fights he left boxing in a dispute with his manager over money.  Dixon met Leonard Caston at a boxing gym, where they would harmonize at times. Dixon performed in several vocal groups in Chicago, but it was Caston that persuaded him to pursue music seriously. Caston built him his first bass, made of a tin can and one string. Dixon's experience singing bass made the instrument familiar. He also learned to play the guitar.  In 1939, Dixon was a founding member of the Five Breezes, with Caston, Joe Bell, Gene Gilmore and Willie Hawthorne. The group blended blues, jazz, and vocal harmonies, in the mode of the Ink Spots. Dixon's progress on the upright bass came to an abrupt halt with the advent of World War II, when he refused induction into military service as a conscientious objector and was imprisoned for ten months. He refused to go to war because he would not fight for a nation in which institutionalized racism and racist laws were prevalent. After the war, he formed a group named the Four Jumps of Jive. He then reunited with Caston, forming the Big Three Trio, which went on to record for Columbia Records.Answer this question using a quote from the following article:

When did he start taking up music full time?
In 1939, Dixon was a founding member of the Five Breezes, with Caston, Joe Bell, Gene Gilmore and Willie Hawthorne.