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

RTM

   1. [Usenet] Read The Manual.  Politer variant of RTFM.

   2. Robert T. Morris Jr.

   The perpetrator of the great Internet worm of 1988 (see Great
   Worm); villain to many, naive hacker gone wrong to a few.
   Morris claimed that the worm that brought the Internet to its
   knees was a benign experiment that got out of control as the
   result of a coding error.  After the storm of negative
   publicity that followed this blunder, Morris's user name on ITS
   was hacked from RTM to RTFM.

   [Jargon File]

   (1995-03-31)


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

RTM
 /R·T·M/

    1. [Usenet: abbreviation for ‘Read The Manual’] Politer variant of RTFM.

    2. Robert Tappan Morris, perpetrator of the great Internet worm of 1988
    (see Great Worm); villain to many, naive hacker gone wrong to a few.
    Morris claimed that the worm that brought the Internet to its knees was a
    benign experiment that got out of control as the result of a coding error.
    After the storm of negative publicity that followed this blunder, Morris's
    username on ITS was hacked from RTM to RTFM.