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

JRL

   J. Random Loser.  The names JRL and JRN were sometimes used
   as example names when discussing a kind of user ID used under
   TOPS-10 and WAITS.  They were understood to be the
   initials of (fictitious) programmers named "J. Random Loser"
   and "J. Random Nerd".  For example, if one said "To log in,
   type log one comma jay are en" (that is, "log 1,JRN"), the
   listener would have understood that he should use his own
   computer ID in place of "JRN".