Ages ago, I bought a job lot of damaged metal marines on ebay. The warlord is based on one of them: his body, arms and head come from the Dark Angels librarian Ezekiel, who came without his normal big sword. I gave my version a plastic sword from a chaos champion, and a backpack and wings from a Blood Angels honour guard. The sword represents a chaos relic called The Murder Sword, which sounds like a concept album by Nick Cave.
There was surprisingly little insignia on the model that had to go: I used some green stuff on the books he's carrying (he is a librarian, after all), but that's all. I mounted him on a bit of scenic base because he's actually rather small compared to the recent plastic chaos marines. I suppose he rules by fear - in an army of people who look like Darth Vader, he looks extremely Vaderesque.