The original idea for a film about Jolson's life was that of newspaper columnist Sidney Skolsky. Jolson was an obvious subject for a film biography after the success of Yankee Doodle Dandy (1942). Warner Brothers were interested in making the film but Columbia got the rights for a five period from 1943.
It was agreed at the start that Jolson wouldn't play himself in the picture.
Harry Cohn, the iron dictator of Columbia pictures was a Jolson fan but he was extremely worried when Al was very ill in late 1944, early 1945. He actually visited Jolson at the hospital asking him : "Are you gonna die on me?" Fortified by injections Al put on what was almost a performance but collapsed when Cohn left.
In March 1945 Cohn got hold of arranger Saul Chaplin and told him: "Take Jolson to the studio and record everything he knows. I want to be insured in case the s.o.b. drops dead."
At first Jolson hadn't been that worried that someone else would play him but as time went by he became more concerned about it. In the weeks leading up to the start of production he asked for the chance to test for the role but never appeared at the appointed time. Perhaps he secretly realised that there wasn't a thing in the world which could make a man who was almost 60 look like a 20 year old.
According to one source Larry Parks was the only actor actually tested for the part. Parks a fairly insignificant B movie actor up to then was perfect for the part and extremely good at miming the songs.
From his first test recording Al proved that he had never sang better in his life. Saul Chaplin though was a little disappointed by the first version of April Showers. Chaplin said Al missed out the recited second chorus and the three syllabled ending. Jolson followed Chaplin's advice and rerecorded the number.
There was no song in Jolson's repertoire for a scene near the end of the picture when Al's parents visit his California home on their wedding anniversary (Al's mother was still alive at this point in the movie). Jolson hummed a Viennese waltz on the set to which Chaplin added a lyric. The Anniversary Song was to be a huge hit.
For one scene in the picture Jolson wasn't happy with Larry Parks' portrayal. This was the scene in which Al was depicted dancing down the Wiinter Garden runway singing Swanee. "The kid just can't do it" said Al, "and nobody can do it except me. Are you going to have a picture about me without Swanee or a Jolson picture without me dancing or whistling ?"
The answer to those questions had to be no so for this one scene in long shot Al Jolson played himself.