Gotrek is a Trollslayer, a dwarf who has so shamed himself that he has shaved his head into a Mohawk and is seeking death in battle to redeem himself in the eyes of his fellow dwarves. This means you will find him wherever the fighting is thickest. Felix is the son of a rich merchant who is trying to escape his family and drunkenly promises to write an epic based on Gotrek's deeds. Therefore he is forced to follow Gotrek from battle to battle and the pair develop a bond as they quash various evil plots around the Warhammer world.
The series starts with Trollslayer and builds from there, like I said before a fun read.