This man was the manager of the Gotham National Bank, which was a front for the city's organized crime families to store their money. When the Joker and his gang of thugs arrived to rob the bank, he was surprised, but remained collected. He discreetly produced a shotgun and managed to kill Chuckles, one of the thugs. Presumably, he also called Sal Maroni and the other Mob Bosses informing them of the robbery.
The manager then made his way through the lobby, taking shots at Grumpy and the Joker (under the alias "Bozo"), who ducked behind counters. In his scheme to kill off his men for all their collected cash, the Joker tricked Grumpy into believing that the manager had run out of ammo. When Grumpy stood to kill the manager he was grazed by buckshot. Discouraged, he ran to the vault.
With the manager's shotgun then unloaded, the Joker sprang up and shot him in the legs. Shortly before the Joker left, the Manager chastised him about how he lacked honor, even by criminal standards, and questioned him what he believed in. The Joker then shoved a canister into the manager's mouth, and revealed his true identity, stating "I believe whatever doesn't kill you simply makes you - stranger". As the Joker drove off with the money and the manager's shotgun, a string attached to the Joker yanked the safety pin out of the canister in the manager's mouth. Instead of exploding, it released fumes of an unknown nature. The manager groaned as his head dropped. It remains unknown if the bank manager was killed or simply knocked out.