Illic Nightspear
Basically, this guy is a fuckold eldar who has followed the path of the Outcast for thousands of years. Over time he has grown fond of bright colors and bad jokes, thus has developed a clown fetish of massive proportions.
He is supposedly looking for lost paths in the webway, which means that he has fostered powerful relations with the harlequins...(mostly the women), leaving thousands of bastards that are almost as badass in the ways of sniping and stealth as he is, known as pathfinders by their more pussy brethren, the lowly rangers. He has a string of broken hearts, pissed off exes, and baby mommas so long that it rivals Vance Motherfucking Stubbs' harem. It would be impressive except that its taken him a fuck billion times longer to do, thus further cementing humanity's glory. On the other hand, Eldar women are probably slower to get into bed or serious relationships (they do have slower gestation periods when they do get pregnant, and conception requires several bouts of intercourse).
Illic sometimes decides to give some of his knowledge of the webway to Craftworld Alaitoc, whose close ties to the Harlequins lures him in for the chance of getting some of that multicolored ass.
The pathfinders whisper that Nightspear is supposed to be off preventing the cataclysm known in eldar legend as the Rhana Dandra, where all of the Phoenix Lords will gather and face their final deaths, but there are so many legends about him, (mostly about how he pursues dat space clown ass), that it is difficult to be sure of his intentions. Regardless, his presence on the battlefield is a great asset to Alaitoc, and he has ended conflicts with his ability to 360 no scope imperial generals, Necron lords, and various other enemies of the eldar with his rifle that can teleport people into the warp.
Inexplicably, despite his fluff, he has neither the highest possible BS in theory or in practice - his rockin' sockin' BS 9 is less than Cypher's 10, and since BS 8 is achievable in mere decades by *humans*, provided they train like they mean it. and BS 9 is only very slightly better than BS 8 when not firing blasts - and less accurate than BS 5 with a gun with two barrels, he's not nearly as capable a shot as his fluff would lead you to believe blame a combination of Gameplay and Story Segregation along with GW's typical favoritism towards humans and/or the Imperium.