Gary Richrath, a former guitarist for the rock band REO Speedwagon who also co-wrote the group’s hit song “Take It on the Run,” died Sept. 13, according to a publicist for the band. He was 65.

Erik Stein confirmed the death but offered no details about the cause or location of death.

Gary Dean Richrath was born in Peoria, Ill., on Oct. 18, 1949. The band formed in the late 1960s at the University of Illinois and came to include Mr. Richrath by the time it released its self-titled debut in 1971. It took years for the group, known for its power ballads, to win a mainstream audience.

REO Speedwagon has released a number of successful albums, including 1980’s “Hi Infidelity,” which sold 10 million copies in the United States. It had two No. 1 hits on the Billboard Hot 100: “Keep on Loving You” (1981) and “Can’t Fight This Feeling” (1984).

Besides “Take It on the Run,” which became a Top 5 pop hit on the Billboard charts, Mr. Richrath was crediting with helping write many other songs for the band, including “Ridin’ the Storm Out,” “Son of a Poor Man” and “Only the Strong Survive.”

He stayed with REO Speedwagon until 1989, exiting amid increasingly tense relations within the band.

Mr. Richrath last played with REO Speedwagon in 2013, when the band performed a benefit concert in Bloomington, Ill., to raise money for tornado victims.

Mr. Richrath released a solo album, “Only the Strong Survive,” in 1992.

No information about survivors was available.