The Free On-line Dictionary of Computing (19 January 2023):

cookie monster
cookie bear

    (From the children's TV program "Sesame Street")
   Any of a family of early (1970s) hacks reported on TOPS-10,
   ITS, Multics and elsewhere that would repeatedly demand "I
   WANT A COOKIE" until the victim typed "COOKIE".

   [Jargon File]

   (1997-02-12)


The Jargon File (version 4.4.7, 29 Dec 2003):

cookie bear
 n. obs.

    Original term, pre-Sesame-Street, for what is now universally called a 
    cookie monster. A correspondent observes “In those days, hackers were
    actually getting their yucks from...sit down now...Andy Williams. Yes, that
    Andy Williams. Seems he had a rather hip (by the standards of the day) TV
    variety show. One of the best parts of the show was the recurring ‘cookie
    bear’ sketch. In these sketches, a guy in a bear suit tried all sorts of
    tricks to get a cookie out of Williams. The sketches would always end with
    Williams shrieking (and I don't mean figuratively), ‘No cookies! Not now,
    not ever...NEVER!!!’ And the bear would fall down. Great stuff.”