I know people tend to associate him with the showier form of country music, but I'm not sure how many people realize how much, as a recording session musician, Campbell influenced a broad range of pop music in the 1960's.
From the obit:
Campbell's guitar acumen and versatility made him an essential player on Los Angeles' thriving recording scene in the 1960s, and he contributed to sessions for Frank Sinatra, Dean Martin, Rick Nelson, The Mamas and The Papas, Merle Haggard and many more. Campbell couldn’t read music, but he quickly became a respected, first-call player. He played on Elvis Presley’s “Viva Las Vegas,” The Monkees’ “I'm a Believer,” Frank Sinatra’s “Strangers in the Night” and more. He played 12-string guitar on the Beach Boys’ “Sloop John B.,” and toured with the Beach Boys in 1965, as a replacement for the band’s troubled and reclusive leader, Brian Wilson.By the way, "Viva Las Vegas" was written by Doc Pomus, who has been profiled in The Coracle, and Campbell was one of The Wrecking Crew, that loose-knit collection of session players mentioned in another profile, that of Carole Kaye, that may also be found on The Coracle.
"I'm A Believer", written by Neil Diamond, was the first song that I ever sang with a band in public. [When testing the sound system in an empty church, I still sometimes sing it.]
I always liked this one by Campbell, written as it was by a serviceman in Vietnam during some rather dark times: