For me it's Thralls with 267 deaths at their hands. Knights are right behind them with 263. Also found it interesting that according to the grimoire, I have never been killed by a Servitor. Fallen gods my ass.
Edit: I take that back. Sepiks Prime has killed me 23 times so there's that. And also Atheon , who has killed me 313 times apparently. Though I'd still put Thralls in first as many of those kills are raid glitches or a team effort (or lack thereof).
-
My trip mine grenade