Oswald Cobblepot-

 You worked at Fish's as a singer.

Edward Nygma-

You took over Miss. Kringle's job after she was killed.

James Gordon

Jim trained you when you joined the GCPD.

Jerome Valeska

Your father worked at Arkham and you visited one day. You ran into Jerome while there.

Victor Zsasz-

You two were sent to kill each other .