Marauder was a spin-off company of Citadel that consisted of at least Trish and Ally Morrison and possibly Colin Dixon. The Marauder label was reportedly formed for tax reasons, with the models actually cast and distributed by Games Workshop. They were advertised in White Dwarf magazine, and carried by the same stories which carried Citadel products.
The line only lasted for a few years, then was disbanded and absorbed into the Citadel lines, with the three artists going back to work for them as well. Some of the older boxed sets - such as the Goblin Wolfriders and the Orc Wyvern Rider and the Bearded Giant - were once Marauder products, later repackaged in Citadel boxes, and at one time had a small "by Marauder Miniatures" logo placed on the covers.