This role typically requires the use of radar, landing lights[?], direction finders to find the airbase at night, and various communications equipment and lighting inside the cockpit. This much gear normally required a twin-engine aircraft to lift it, notably because this left the nose area of the plane clear for the radar installation, where the engine would be in a single-engine design. Many night fighters were converted from earlier heavy fighter designs, and some from bombers.
During World War II the Luftwaffe also experimented with single-engine planes in this role, which they referred to as Wilde Sau (wild boar). In this case the fighters, typically Focke-Wulf Fw 190s, were equipped only with a direction finder and landing lights. In order to find their targets other aircraft, guided from the ground, would drop strings of flares in front of the bombers, or simply wait for them to fly over the burning cities below.
Night fighters existed as a separate class into the 1960s. As the aircraft grew in capability, the role interceptor was often one and the same as night fighter, due to the same plane having both the speed and radar needed to fill both roles. Examples of these interceptor/night-fighters include the Avro Arrow, Convair F-106 Delta Dart, and the English Electric Lightning.
Continued aircraft development has blurred this line even further, to today where there are no longer designs dedicated to this role because "normal" designs have all the capability needed. The only designs remaining in service in this niche are the US Navy's F-14 Tomcat and the Russian MiG-31[?]. In both cases they have needs to support operations at very long ranges – out of missile range for the Navy, and across Siberia for the Russians – which cannot be filled by smaller aircraft.