MEMPHIS, Tenn. (AP) — It’s 1966 and a thunderstorm illuminates the night sky in Memphis, Tennessee. Two Stax Records musicians, guitarist Steve Cropper and singer Eddie Floyd, sit in a room inside the Lorraine Motel, struggling to fashion a song about love and superstition.

The pair try many references to good and bad luck — rubbing rabbit’s feet, breaking mirrors — but nothing fits. Then, as the lightning flashes and the thunder roars, Cropper asks Floyd: “What do people usually do for good luck?’”

“And Eddie goes, knock, knock, knock,” Cropper told The Associated Press. “I said, ’There’s our song, ‘Knock on Wood.’”

At a time when it was common for white musicians to co-opt the work of Black artists and make more money from their songs, Cropper was that rare white artist willing to keep a lower profile and collaborate. That may explain why now, more than half a century later and still making music at 79 years old, he can walk through an airport or a grocery store without being recognized, while the original songs he co-wrote — played on sound systems in those same public spaces — remain instantly familiar.

From “In the Midnight Hour” to “(Sittin' On) The Dock of the Bay” to “Soul Man,” Cropper worked alongside the likes of Otis Redding, Wilson Pickett, Isaac Hayes, Sam and Dave, Eddie Floyd and many others to leave an indelible imprint on the American songbook.

Missouri-born and Memphis-raised, Cropper joined the Stax Records team as a 20-year-old. Working as a songwriter, producer, and guitarist in the bi-racial house band Booker T. and the MGs, Cropper laid the foundation for songs that have outlasted the studio that created them.

“Knock on Wood” featured Cropper’s catchy, hip-moving guitar and rousing horns, setting the stage for lines still heard heard in TV commercials and movies: “It’s like thunder and lightning, the way you love me is frightening. I better knock, on wood, baby.”

Cropper draws a lean, precise, understated-yet-signature sound from his guitar. “In the Midnight Hour,” “Soul Man,” and “Time is Tight” feature irresistible intros. Cropper mastered the art of filling gaps with an essential lick or two, then stepping aside as organist Booker T. Jones, bassist Donald “Duck” Dunn and others led the way.

“I listen to the other musicians and the singer,” Cropper said. “I’m not listening to just me.”

On a YouTube instructional video, guitar virtuoso Joe Bonamassa says Cropper’s moves are often copied.

“If you haven’t heard the name Steve Cropper, you’ve heard him in song,” Bonamassa said.

As a teenager new to Memphis, Cropper fell in love with music emanating from churches, clubs and car radios. He bought his first guitar from a Sears catalog at age 14.

Formed by Jim Stewart and Estelle Axton, Stax Records became a soulful, gritty counterpoint to Detroit’s Motown. Booker T. and the MGs, with Cropper, Dunn, Al Jackson and Jones, became the lead house band. When trumpeter Wayne Jackson and saxophonist Andrew Love joined them, they called themselves the Mar-Keys.

Cropper, Dunn and Wayne Jackson were white. Jones, Al Jackson and Love were Black.

“When you walked in the door at Stax, there was absolutely no color,” Cropper said.

In 1962, when Johnny Jenkins and the Pinetoppers arrived at Stax to record, a valet named Otis Redding was with them.

As Cropper tells it, Redding pestered Al Jackson to ask Cropper to hear him sing.

“He starts singing, ‘These Arms of Mine.’ And I went ‘Holy s---,’” Cropper said. “My hair stood up on my arms. I said, ‘Stop right there.’ He said, ‘What you don’t like it?’ I said, ‘No, I love it.”

The song became Redding’s first hit for Stax, and the beginning a string of hits. In 1967, Cropper and Redding sat down to write “(Sittin’ On) The Dock of the Bay."

As they worked, Cropper decided the song needed something. He went to a Memphis studio known for producing jingles and recorded sound effects of sea gulls and ocean waves.

The song became Redding’s biggest hit.

Cropper left Stax in September 1970. He has has lived in Nashville for more than 30 years. He still cuts guitar dubs at RCA Studio 3, and has a new album set for release in April.

The last time he saw Redding was on a Friday at the studio as he was putting the finishing touches on “Dock of the Bay.”

“He popped his head into the control room. At the time, I was setting up to do the guitar licks,” said Cropper. “Otis said, ’I’ll see you Monday. I said, ‘Ok, I’ll see you Monday.’ That’s the last word I heard from him.’”

Redding, 26, and four members of his band died in a plane crash on Sunday, Dec. 10, 1967. They were headed to a show in Madison, Wisconsin, when their plane plummeted into a frigid lake.

Cropper and his bandmates were in an Indianapolis airport when they heard Redding died. Songwriter David Porter had called his wife, who broke the news to her husband.

“David Porter looked like he had the blood drained out of him. We said, ‘David are you alright, what’s the matter?’ So, he said, his wife just told him that Otis’ plane had gone down, and he had died,” said Cropper, his voice cracking. “Pretty heavy duty.”

Redding never got to hear Cropper’s final version of “(Sittin’ On) the Dock of Bay.”