A member of any website (in this case, a Neopets user) who sends death threats for fun/amusement. Death threat senders risk being iced (having their accounts disabled, or frozen) just to see little girls squeal and start Neoboard topics about how they're going to die.
Usually, Senders lurk on the Neoboards. Clicking on random (or not-so-random) usernames, they copy/paste threats and send them. Later on, the Senders watch as the people they sent threats to panic, comment on their threats, try to seek them out, or threaten to report them.
-Teddy (letters were called 'Teddy letters')
-L (based threats on plot of the manga 'Death Note')
*(based on the Naruto characters, of course)
-Kira (also based threats on 'Death Note')
The above Senders are all members of the FC, or 'Fan Clubs'. Unusually chaotic, these boards are the best targets for Senders. -hinthint-
"I just got the creepiest Neomail from a guy named L..."
"He must be a Sender."