Rockin' Reggie Vincent (real name Vinson) was a friend of the original band for many years and helped out on occasion playing guitar, and co-writting 'Billion Dollar Babies'.
Nowadays Reggie is a preacher and has recorded over 16 albums of gospal music. His autobiography was released in 2018 called 'Still Got A Song In Me: Looking Through The Eyes Of A Rockin' Life' which you can get via his website.
This from Reggie's own page:
"I was in L.A. in 1970 when I met a guitar player named Glen Buxton at some night club or other. He told me he played in a five piece band named 'Alice Cooper'. I thought it was a girls band... far from it! Glen and I had a few beers and were instant friends. We roomed together, we rocked together and we partied together on and off for 28 years.
'Killer' was the first album we did together: you can find my background vocals on 'Be My Lover'. The second album was 'School's Out' and the front cover of the album had a school desk with the band members' initials carved into it. On the same album, the credit for my guitar work and background vocals reads "Special Guest Rockin' Reggie Vincent": I worked on 'No More Mr. Nice Guy', 'Looney Tune', 'Public Animal #9'... out of the 9, I worked on 5 songs. We were all good friends. I became like the sixth Coop. GB and I roomed together in New York. After we finished that record we flew to Puerto Rico and me, GB and Michael Bruce wrote some more songs. We later partied at the casinos with Ron Wood, now the Rolling Stone's guitarist, and lost all our money. That was our very first gold record, and the beginning of a great friendship. I co-wrote 'Billion Dollar Babies', played and sang on that album, and also did some background vocals on their last album 'Muscle Of Love'.