Involvement with the Eagles
Bob Seger, best known for the hits "Night Moves," "Like a Rock," and "Old-Time Rock'n'Roll," was an up-and-coming musician in Detroit when Glenn was starting out there. He took Glenn under his wing and let him play and sing on the single Heavy Music (1967) and on his record Ramblin' Gamblin' Man (1968), as well as encouraged him to write his own music. He also produced and co-wrote the single for Glenn's early Detroit band The Mushrooms. The two remained friends after Glenn achieved success with the Eagles. The Eagles even occasionally covered Seger's Big River during live performances.
Heartache Tonight came about one night when they were hanging out together. Glenn says that whenever Seger was in Los Angeles, he'd pay him a visit and play him stuff he was working on. Glenn would do the same. He played a rough version of Heartache Tonight for Seger, who came up with the chorus off the cuff as they were jamming.