IIRC it was for completing all of the raids in one of the last few expansions, though I don't remember which one specifically.
Not a warrior suffix, a druid mentions he has the title back a few years ago and put together a page on suffix/prefix but guess he never got around to figuring that one out.
Pretty sure it was from the Rain of Fear raid for Chelsith Reborn, prefix Lionhearted for completing the raid...suffix 'the Lionhearted' for server first.
I dont recall there being prefixes for rof raids only suffixes for server firsts. Chelsith was champion of the people iirc