Outlaws are encountered during the What Lies Below quest. In the quest you are required to kill 5 of them. They can be a good way for players to train magic, as they are easy to kill and they respawn quickly.
They sometimes use the phrase "Stand and deliver!" before dealing damage, implying that they are similar to highwaymen or muggers.
They take only 2 seconds to respawn which makes it the fastest item/monster to respawn, excluding the poisonous spider that inhabits Ape Atoll in the temple, which respawns in nearly a second.
They are one of the few NPCs to use the current weapon looks.