Answer by taking a quote from the following article:

Robert Clark Seger (, born May 6, 1945) is an American singer-songwriter, guitarist and pianist. As a locally successful Detroit-area artist, he performed and recorded as Bob Seger and the Last Heard and Bob Seger System throughout the 1960s. By the early 1970s, he had dropped the 'System' from his recordings and continued to strive for broader success with various other bands. In 1973, he put together the Silver Bullet Band, with a group of Detroit-area musicians, with whom he became most successful on the national level with the album Live Bullet (1976), recorded live with the Silver Bullet Band in 1975 at Cobo Hall in Detroit, Michigan.

After Cameo-Parkway folded, Seger and Punch began searching for a new label. In the spring of 1968, Bob Seger & the Last Heard signed with major label Capitol Records, turning down Motown Records, who offered more money than Capitol. Seger felt that Capitol was more appropriate for his genre than Motown.  Capitol changed the name of the band to The Bob Seger System. In the transition between labels, guitarist Carl Lagassa left the band and keyboard player Bob Schultz joined. The System's first single with Capitol was the anti-war message song "2 + 2 = ?", which reflected a marked change in Seger's political attitudes from "The Ballad of the Yellow Beret". The single was again a hit in Detroit and hit number 1 on radio stations in Buffalo, New York and Orlando, Florida, but went unnoticed almost everywhere else, and failed to chart nationally in the US. The single did, however, make the Canadian national charts, peaking at #79.  The second single from The Bob Seger System was "Ramblin' Gamblin' Man". It was a major hit in Michigan, and it also became Seger's first national hit, peaking at #17. The song's success led to the release of an album of the same title in 1969. The Ramblin' Gamblin' Man album reached #62 on the Billboard pop albums chart. Glenn Frey (later in the Eagles) had his first studio gig singing back-up and playing guitar on "Ramblin' Gamblin' Man".  Seger was unable to follow up this success. For the next album, singer-songwriter Tom Neme joined The System, ultimately writing and singing the majority of the tunes featured, for which the group was heavily criticized. The album, called Noah (1969), failed to chart at all, leading Seger to briefly quit the music industry and attend college. He returned the following year and put out the System's final album, 1970's Mongrel, this time without Tom Neme. Bob Schultz left the band as well, being replaced by Dan Watson. Mongrel, with the powerful single "Lucifer", was considered to be a strong album by many critics and Detroit fans, but failed to do well commercially.

who else was in the band?
In the transition between labels, guitarist Carl Lagassa left the band and keyboard player Bob Schultz joined.