Board Thread:Warhammer 40k General Discussion/@comment-25869775-20150126002257

I'm reading Pandorax by C Z Dunn and there is a scene where a Grey Knight is fighting a purple Lord of Change and during the fighting, as they are taunting each other verbally the Lord of Change reveals that he took part in the Heresy. He says.

"I was far from idle, Space Marine. I helped bring half a Legion under the sway of the Four True Gods and took part in the destruction of their home world when their faith was found wanting. I looked on while a primarch died, content in the knowledge that I played a part in his downfall."

So who is this Lord of Change? Which Legion was it that he swayed to chaos and saw their home world destroyed? And what Primarch did he help get killed? May not be the primarch of the legion he helped turn to chaos, but it may be. Thoughts? 