However, despite their banishment, the Jarl's guards established the Dawnguard and continued their vampire-hunting throughout Tamriel. Unfortunately, the Jarl banished his guards after having to kill his son. The Jarl of Riften built Dawnguard originally as a place to imprison his son, who contracted Vampirism. Interestingly, the Dawnguard found their specialization early on. Players of Skyrim will remember Fort Dawnguard in the Velothi Mountains and its occupants, the vampire hunters.
As long as hostile Vampires exist in Tamriel, the Dawnguard will hunt them down.