“(Sittin’ On) The Dock of the Bay” was released 50 years ago Monday, less than a month after Otis Redding died at the age of 26. The song was a departure for the R&B superstar — and it almost never saw the light of day.

“Otis had had a throat operation in the fall that year, and he was very worried about whether he would be able to sing again — and sing like Otis,” biographer Mark Ribowsky says. “He needed to sort of make it quieter, make it more poetic. And he came up with this song.”

The song was an experiment: It wasn’t R&B, it wasn’t rock, it wasn’t folk. At least one executive at Redding’s label, Stax, didn’t get it. “Al Bell heard it being recorded that day and said, ‘I don’t know if we can ever release this song,’ ” Ribowsky says.

They left the recording incomplete that winter. Then, tragedy struck: Redding died in a plane crash on Dec. 10, 1967. While the music world mourned, Stax began planning.

“Let’s face it: When a rock ‘n’ roller dies, you need a song to come out immediately to cash in on this. That’s just the way the business is,” Ribowsky says. “Steve Cropper, who wrote [the song] with him and produced it — great guitar player — said, ‘Let’s do this song.’ “

“I mean, I got this call on a Monday, and of course Otis’ plane went down on a Sunday morning,” Cropper told NPR back in 2000. “And they said, ‘Get that thing finished and get it to us.’ So, I went to work on it. And probably the music is the only thing that kept me going.”

Cropper sent back a completed version within a week. It didn’t take at first.

“Jerry Wexler up in New York at Atlantic, the overlords of Stax, said, ‘No, we can’t release this. His vocal is too recessed. It needs to be remixed,” Ribowsky says. “Cropper said, ‘OK, I’ll change it: I’ll overdub it, I’ll do this, I’ll do that’ — [and] didn’t change it whatsoever. Sent it back to Wexler, who said, ‘Oh yeah, this sounds a lot better now.’ “

“(Sittin’ On) The Dock of the Bay” went on to win Otis Redding two posthumous Grammys and sell millions of copies, becoming his signature song and his biggest hit.