Help! Which God?

[Lord Manton]

Loungers and esteemed scholars, I need your help.

I'm looking to expand and more tightly theme my Iron Warriors warband, but I just can't fix on which god would fit best with my ideas.

It's a two pronged army: There is a Terminator Lord leading a band with a couple squads of marines, backed up by a vindicator, a predator and probably another HS choice in the form of a tank. A fairly standard Iron Warriors situation.

Then alongside this, I want a separate detachment with a Warpsmith, a couple units of cultists (who will be modelled to look like dark skitarii or servitors) and backed up by a few daemon engines (forgefiends, defilers etc).

The idea is that the Warpsmith is a deranged mad scientist who experiments on captured Imperiels creating unholy fusions of man/machine/daemon.

So what do y'all think would fit my theme?

PS. I am open to the two forces worshipping different (obviously not enemy) gods.

[DrBored]

Of the four Chaos Gods, Nurgle jumps out. That doesn't mean you have to get a bunch of pustulent mushroom-ridden plague marines or anything, but you could use the rules for Mark of Nurgle and Plague Marines to run Iron Warriors that have been so heavily modified and upgraded that they literally feel no pain, and are literally tougher than the rest. A mad scientist would totally work towards that sort of goal on his own Marines.

Beyond that, Slaanesh comes to mind, and drugs and stimulants totally fit the mad scientist M.O. Slaanesh Bikers with the Icon of Excess are actually MORE survivable than Nurgle Bikers against things like Plasma Guns and Melta Guns.

Khorne and Tzeentch don't really fit the theme, but would be a neat antithesis if you were looking to 'round out' your army with variety, but it sounds more like you're trying to stick with a theme.

[0rph3u5]

The problem with picking a Chaos God is that it is question of motive not action; thought the Chaos Gods each favour certain actions, they are powered by some emotional drive behind these actions. Since you have given only the achetypes of your warband leaders and not a motivation it is hard to give you a good answer.

Tzeentch:
The "mad scienist" theme could very well be Tzeentchian, esspecially if the ritualistic binding of Daemons is involved. After all, the experiments on the Imperials might be done as a deranged quest for knowledge which the Changer of Ways looks favourable upon - not as favourable as a quest for psykic power and lore but still, knowledge is (almost) everything to Tzeentch.
As for the Terminator vanguard ... Depending on the Lord motivation it might be very well Tzeentchian as well: Leading a group of competeing champions into battle to see which one emerges as the most ruthless and cunning isn't unheard of (see Storm of Iron) - here being the master manipulator is the prime objective.

Slaanesh:
Slaanesh is empowered by excess and the drive for perfection and novelity - Both might work here for your champions. Driven by the thrist for creating novel contraptions (with novelity being foremost before anything else) your Warpsmith might do his experiments and build his daemonengines and test them on the battlefield. Your Lord might be driven by the wish to plan and perfrom the perfect siege or defense which fits neatly with Iron Warriors.

Khrone:
Khrone might work as well. While the Lord of Blood looks most favourful on enraged hand-to-hand combat, all aspects of warfare conducted for the sake of warfare and bloodsheed, out of rage or as a quest for vengence are favoured by Khorne.
Here the motivation of your champions would be to kill for sake of killing or to prove themselves superior (but not perfect) to the enemy, their god/daemoic patron and/or a rival.
EDIT: alternatively the organisation of test of new contraptions as blood sport might be something a Khronate Warpsmith would od.

Nurgle:
That works not so well on the "fusion of man/machine/daemon". Nurgle is empowered by the fear of death and disease which makes many of his followers embrace his pestilences as a paradox way to become immune to sickness and be free of death. The way to embrace the machine as a means to become immune to physical harm competes with that philosophy.

On the other hand it might work if your champions see themselves as harbingers of death and fear; but that is rather Night Lords territory than Iron Warriors.

[Katharon]

Iron Warriors have tended to be removed from worshipping any one particular Chaos God. I'd say either Nurgle or Khorne seem to suit them far more than either Tzeentch or Slaanesh. This is, of course, if you're going for a strong fluff feel. You can also always take a look in the Homebrew section of the forums where there is an Iron Warriors homebrew supplement that is, apparently, popular in Germany at the moment.

[Lord Manton]

The Iron Warriors as a legion have no specific affiliation, but different war bands are well documented as having leanings to and worshipping particular gods. In Angel Exterminatus for example Kroeger slowly descends into Khorne worship as the novel progresses and in the Ultramarines novel based on Medrengard, there is a Warsmith using Tzeentchian sorcery against Honsou. So there is precedent for worship of the Gods, it's just particular to each Warsmith.
I've often thought about using the Mark of Nurgle to have the toughness element for the IW's use of bionics, but as it's just shoe-horning a buffing mechanic with no fluff, it doesn't sit well with me. I like the idea of Khorne as Berzerker maniacs charging in to bust a siege. And the idea of using all the pretty Khornate daemon engines on offer.
I think I might just have to go with Undivided in terms of my Warpsmith, though. He's got a strong Fabius Bile influence, and Bile only seems incidentally aligned to Chaos.