Author of handy utils like crontab, and others. Paul Vixie (sometimes just called Vixie) has been contributing Unix utilities and net protocols since 1980.

People today probably know him for the MAPS RBL, a blacklist for spammers. Admin types probably know him due to his authorship of BIND, an open source DNS implementation popular on many flavors of Unix.

Contributed to the books Sendmail: Theory and Practice and Open Sources: Voices from the Open Source Revolution.