Mordrak - what is best to represent him?

I need to build me a Mordrak - mainly so I can put together a force that hasn't yet fully formed in my mind

But...what to use?

All suggestions welcomed!

I built my Mordark from the GKT box set, as a standard Terminator Justicar with hammer and a bare head.

SJ

I built mine with a custom made two-handed hammer, some SM bits and BA bits, but the main body was a GK Termi. Best models so far.

Paladin Justicar w/ a daemonhammer and a lot of purity seals etc should do it.

For my Mordrak I used a terminator chaplain as the base model. I replaced his arms and shoulder pads from the grey knight terminator box set and used a hammer from it as well. Threw on some purity seals and as his storm bolter I used the one from a dreadnaught kit (just because I like the ammo chain). There are plenty of interesting ideas floating around on google, but I like the idea of a skull helmet to represent his fallen comrades. And it stands out from the ghost knights and the rest of the army. Now I haven't really put the ghost knights together but I plan on using the older oop metal grey knight terminators.