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).
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.