Larry Wall is primarily known today as the author of
Perl, a
scripting language that gradually grew into the more serious
programming language it is today.
Wall is a linguist by education, i.e. trained to study natural language; this background shows in Perl, particularly in its very free mixing of statements and expressions, and its very free
use of statement and expression connectives, giving the programmer much
liberty in expression:
if ($a > 0) { ++$b; } # if $a is positive, increment $b by one
++$b if $a > 0; # the same
$a > 0 and ++$b; # the same again
Little if any of this
idiom was invented in Perl; most of the language was borrowed from other languages, which is another trait it shares with natural language.
Larry Wall also wrote patch, a program that takes a set of differences between two sets of text files, and applies it on the first set to recreate
the second set. Such a set of differences is itself known as a patch, and
it is the standard way to distribute changes to the source code of a computer program; for example, changes to fix bugs in the program, or to add a new feature.
He also wrote rn, the first serious newsreader, later continued as trn and strn, I still use trn, although many other Usenet clients are more popular today.
Wall is a verbose person: he likes language and is quite pleased with himself, which is apparently a contagious condition. To this we owe the fact that Perl, Perl documentation and anything else written by the same guys is not only useful, but also fun to read. Compare the Perl install-time configuration session to the average ./configure session, or the average perldoc page to the average manpage, and you'll see what I mean.