Gus was a former post office worker working with Dwight Pollard to resurrect the dead.
Dwight Pollard goes down to their secret lab, where he scolds Gus for letting a revived Melanie Blake get loose and be found dead. Gus claimed that Melanie stumbled out while he wasn't looking and died again when her body couldn't take the electrical currents that were placed into her which proved to be too strong. The pair of them come to the conclusion that it is time to resurrect Jerome Valeska.
When Dwight is informed by Gus about Andrew Dove's tip-off that James Gordon leading the police to their location, he suggest they abandon the project only for Dwight to shock him with an electrical wire. The police later found his dead body.