Horned Rat
The Horned Rat is the festering disgusting god of the equally disgusting Skaven race in the Warhammer Fantasy setting. Think of what happens when the Machiavellian backstabbing genius of Tzeentch mates with the ratty repulsiveness of Nurgle.
Spreader of AIDS and STDs, rolling around in his own muck, the Horned Rat only exists to troll his own worshippers and the rest of the world and to tear down civilization, the arts, anything remotely good and replace it with his own favourite pastimes (namely disease, backstabbing, and cruelly toying with others).
As you can expect, no one likes him and he is the archenemy of several gods, particular Sigmar and Sotek. The only reason he hasn't been curbstomped and fumigated is because he has perhaps more worshippers alive then any other god in the setting and this gives him a blotted amount of power (and a needless sense of self-importance). Granted each individual skaven isn't worth squat but put enough together and it gives him enough power to be a major god of the underworld.
However, he doesn't do anything, as he is too busy getting eaten by Sotek or his head smashed in by Sigmar's hammer.
Once his divine majesty deigned to make an appearance, to end one of the civil wars that was tearing his people apart. Summoned by the Grey Seers, he ate a few skaven, gave them a telling off, ate a few more and then left some pillars of warpstone behind with instructions on how to backstab and bitch better in his name. And no word of him since them.
The Horned Rat keeps going on about a great plan to take over the world and passes it onto his Grey Seers for them to tell the masses but this is really just a tool to keep the Skaven in line and generally striving towards the Rabid Rat's goals. Needless to say, once (if) the Skaven do take over the world, then the Horned Rat will swoop in, thank them for their hard work and then eat them all, satisfied he has finally won (just as planned).
He has his own greater daemons, the Vermin Lords, who are renowned trollers who give any skaven and others quite rightly the creeps. It is one of the toughest units a Skaven force can wield, combining powerful magic, strong combat skills and general unpleasantness into one hideously glorious model.
Considering his penchant for scheming he is probs Tzeentch's pet rat that got too much of an ego boost and decide to go it alone. Although equally possible with his connection to disease he is Nurgle's test subject and is taking out his pain through others. Khorne regularly tries to stomp on him since he despises cowards and well...does Khorne need a good reason to get angry? Slaanesh meanwhile constantly has strange ideas about what to do with the Horned Rat that for reasons of mental sanity cannot be repeated here.
Whatever the case is, other chaotic beings look down on the Skaven and the Horned Rat as mere vermin, perhaps useful to a degree but not worthy of respect and they are usually killed on sight. And this is what other chaos races think of the Skaven. So being a ratman is not a good sell.
Should you see a Horned Rat in your area, call your local fumigators to get rid of the problem. Nothing ruins a day like a nasty ratmen infestation.
One interpretation is that the Horned Rat is actually a guise cooked up by Tzeentch to create his own exclusive race of mortal worshippers. Let's see; a race driven entirely by ambition (Tzeentch's fuelling emotion), that prizes constant innovation (Tzeentchian doctrine), noted for its embrace of both constantly changing technology AND rampant mutation/biomanipulation (more Tzeentchian doctrine/methodology), with a creedo of being the ultimate survivors and manifest destiny (you see where I'm going here, right?)...
The only possible dissension is the existence of Clan Pestilens, which reveres the Horned Rat as a spirit of disease, decay and ruination. But this is still compatible with the interpretation above when you remember Clan Pestilens and its doctrine came after Clan Pestilens was trapped in Lustria for multiple generations and had a "revelation into the true nature of the Horned Rat", and that the other Skaven considered Clan Pestilens as heretics when they first returned and still regard them as heretical to some extent today. This suggests, then, that Tzeentch made the Skaven first in his guise of the Horned Rat, and then Nurgle took on the Horned Rat's guise himself to try and stick his grotty fingers in Tzeentch's pie by luring the Skaven into worshipping him instead.
End Times
The Horned rat once again makes an appearance in the End Times. This time, he speaks directly to the council of 13 and tells them to cut the shit and stop all the infighting. The World was ripe for the taking and the skaven would be the ones to conquer it, as a whole united race. He incinerates the current seer of the council and has him replaced with one who will supposedly speak directly from the Horned Rat himself... Thanquol. Yes, that Thanquol. The drugged up failure of a rat, so incomprehensely incompetent he could only function as "that one guy who tries a lot to be evil and cool but fucks up all the time because of how fucking stupid he is". Kinda like most of you guys in High School, oh snap!
Anyway, for the first time in history, the Skaven are truly united, and rise to the surface in the millions at the command of the Horned Rat. They then take the role of the tyranids and squat Estalia, Tilea, and the border princes with Araby next on the list.