From The Jargon File (version 4.4.7, 29 Dec 2003):
ken
/ken/, n.
1. [Unix] Ken Thompson, principal inventor of Unix. In the early days he
used to hand-cut distribution tapes, often with a note that read “Love, ken
”. Old-timers still use his first name (sometimes uncapitalized, because
it's a login name and mail address) in third-person reference; it is widely
understood (on Usenet, in particular) that without a last name ‘Ken’ refers
only to Ken Thompson. Similarly, ‘Dennis’ without last name means Dennis
Ritchie (and he is often known as dmr). See also demigod, Unix.
2. A flaming user. This was originated by the Software Support group at
Symbolics because the two greatest flamers in the user community were both
named Ken.