Pete Ustinov was David Nivens batman durning WWII.
A batman's duties often include:
- acting as a "runner" to convey orders from the officer to subordinates
- maintaining the officer's uniform and personal equipment as a valet
- driving the officer's vehicle, sometimes under combat conditions
- acting as the officer's bodyguard in combat
- other miscellaneous tasks the officer does not have time or inclination to do
The action of serving as a batman was referred to as "batting". In armies where officers typically came from the upper class, it was not unusual for a former batman to follow the officer into later civilian life as a domestic servant.