Believed to have arrived in the Tallowlands from another realm, the rat-scientist known as the Great Skritt has long harboured plans to dominate the Underland. Having manipulated, bullied or outright murdered a sufficiently impressive number of lesser engineers, he formed the notorious Skryrenet in order to harvest resources and influence warlords across the realm. This culminated in the Skaven Dread Council putting military decisions into the claws of Skryrenet, whereupon Skritt instigated a series of simultaneous civil wars designed to eliminate all power structures across the Skaven-held Underland and deliver full control to him.
His plan was close to succeeding when, desperate, the Skaven of the Dar'Koath caverns forged an alliance with the surface clans. An army of overland warriors led by Yan of the Connaghi entered the Underland and eventually destroyed Skryrnet's defence grid, causing Skritt to flee.
An unintended consequence of this was that the Underland goblins, previously weakened by their own infighting, saw opportunities to expand and a significant amount of territory was lost to goblin factions. Yan Connaghi remains in the Underland to this day, aiding the Skaven clans in battle against the goblins.
The Great Skritt disappeared for a period of time but has recently reemerged and seeks to rebuild Skryrnet. He seeks caches of warp-emerald, a potent energy source which will allow him to power a time-travel device he has built. Once he has enough warp-emerald to generate thirteen kilo-ratts of power* he will send the being known as the Verminator back in time to prevent Yan Connaghi from being born.
He believes that the fall of the Sinian Empire has left vast troves of warp-emerald free for looting. In particular, it seems that areas home to many Undead beings ("Gribblians", as they are known in the Skaven tongue) are rich in warp-emerald. Indeed, he has identified a Gribblian Terrorgheist whose hoard is likely to contain all the warp-emerald he needs.
Skritt is always accompanied by his pet, a well-trained rat called Morty McFlea. He intends to use McFlea to conduct the test run of his device.
It has been rumoured that, while on the run from the Connaghi, Skritt stole an item of value from the Underland goblins. The nature of this item is as yet unknown.
*Author's note: this is the power required to propel the device at a speed of eighty-eight miles per hour.