Gnus was originally written by Masanobu UMEDA in 1988, I believe, and went through a series of releases up until 1992.
I started a rewrite of GNUS in late '94. The most important thing about a rewrite is to find a neat name. «Warp GNUS NT: TNG Six.0 for Windows» was my first attempt, but someone suggested «(ding)», so I went with that instead, until we decided that «Gnus» is really a perfectly good name. So we went back to that one, but without caps.
Having gotten the difficult part over with, I set out to change GNUS into what I wanted it to be: fast, flexible and tidy. At the same time, I really liked GNUS, so I didn't want to change the user interface much, except to make it more straightforward.
Gnus is supposed to work as a drop-in replacement of GNUS. Casual users shouldn't notice anything much - Gnus understands GNUS startup files and variables. Most functions have kept their names. Almost all key-bindings are the same. However, internal structures have been completely redone, so if you have written clever functions that rely on anything but the most top-level commands, your code will fail.
The first "proper" release of Gnus 5 was done in November 1995 when it was included in the Emacs 19.30 distribution (132 (ding) Gnus releases plus 15 Gnus 5.0 releases).
In May 1996 the next Gnus generation (aka. "September Gnus" (after 99 releases)) was released under the name "Gnus 5.2" (40 releases).
On July 28th 1996 work on Red Gnus was begun, and it was released on January 25th 1997 (after 84 releases) as "Gnus 5.4".
Quassia Gnus was the next release.
From The Puffin Joke Book.
It was released as Gnus 5.6.
Then came Pterodactyl Gnus, which has now been released as Gnus 5.8/5.9.
Oort Gnus was started in October 2000. It's big, it's way out there, and it occasionally rains down death and destruction on innocent bystanders.
Oort Gnus was released as Gnus 5.10 in May 2003 - and Gnus 5.11 bundled with GNU Emacs 22.1 in June 2007.
Work on the following development version, dubbed No Gnus, was begun in January 2004. A version of No Gnus was released as Gnus 5.13 with GNU Emacs 23.1 in July 2009.
More information about versions can be found in the manual.