The Free On-line Dictionary of Computing (30 December 2018):

Knights of the Lambda-Calculus

   A semi-mythical organisation of wizardly LISP and Scheme
   hackers.  The name refers to a mathematical formalism invented
   by Alonzo Church, with which LISP is intimately connected.
   There is no enrollment list and the criteria for induction are
   unclear, but one well-known LISPer has been known to give out
   buttons and, in general, the *members* know who they are.

   [Jargon File]