Only two pilots are needed to fly the Airbus A380. However, for long haul flights (usually flights more than 7 hours in flying time), a relief crew will be carried in order to allow the original flight crew to rest while in flight. read more
It does not have to have four pilots. But all aircraft on very long flights carry a second crew so that one crew does not have to be on duty for too many hours. The A380 is mostly used for long flights so will usually carry a second crew. read more