In the Prologue you can find a lot of different enemies patrol the zone or in specific zones.
The Junkies are a specific type of enemies that you can find walk randomly on the map. The Junkie will insult you if you walk near to him, and this enemy only will attack you if you walk close to him. The Junkie doesn't have high damage or epic skills, just will jump and attack with punches and kicks. In general, is a weak enemy.