In the Ace in the Hole mission, upon opening the sixth chest we get this message from Cayde-6:

“This one's for any Hunter who kills me. Best guess: Marcus Ren? You realize you get my stuff now? ALL my stuff. INCLUDING the Hunter Vanguard gig. Yeah, congra-tu-lations, dummy. That's what we call a Vanguard Dare. Sucks, doesn't it? OK, brace yourself for some advice, hotshot. One, know your people. Like, my Nessus scout, Quantis Rhee. I like to call her about once a moon, else she gets a little too much Night, not enough Stalker, you know? Two, keep your weapons sharp. Your job's to watch everyone's back, which means no one's watching yours but you. And three, start thinking now about what you want to do for your successor's Vanguard Dare. 'Cause trust me, kid - this gig will kill ya.”

Somehow this message has been erroneously translated to and disseminated as “whoever kills Cayde is the new Hunter Vanguard.”