Sir Dystic
The cDc member who wrote Back Orifice, the remote-control tool that showed how little Windows 98 defended itself.
Josh Buchbinder, a.k.a. Sir Dystic, released Back Orifice at DEF CON 6 in August 1998. It gave complete remote control of a Windows 95/98 machine — files, keystrokes, screen — and the name was a jab at Microsoft BackOffice. The group called it an administration tool; the antivirus industry called it a trojan. Both were right, which was rather the point.
Microsoft replied that it posed no threat because the user had to run it first, which in practice was exactly how malware spread. The sequel, BO2K (1999), was written by DilDog and released as open source.