Warhammer 40,000: Codex Imperialis (1993), p88 — Chaos Champions

Although we divide Chaos Space Marine characters into Champions, Heroes and Mighty Heroes for convenience, all of these characters are termed Chaos Champions. Chaos Champions are the favoured servants of their masters, the Gods of Chaos, and their complete devotion is rewarded with numerous gifts of power.

As a Champion gains favour in the eyes of his Chaos God so he becomes more powerful. There is a terrible price to pay, for the Gods of Chaos are whimsical and uncarign creatures, whose gifts often bring gross physical mutation and deformity. Horns, wildly discoloured flesh, distorted limbs, cloven hoofs and other, stranger, mutations are all too common amongst the Champions of Chaos who bravely bear their disfigurements as symbols of their divine favour.

Nurgle

Champions of Nurgle are swollen with corruption, their armour barely containing their bloated bodies. Because their bodies are dulled with disease and partly rotted away they feel little pain and can endure considerable injury without discomfort. A Chaos Champion of Nurgle always adds an extra +1 to his Toughness on account of his hugely bloated body.