Introduced in CS 1.1 on the 13th of March, 2001, created by the one and only David Johnston (who had created the original Dust and later created de_sienna for CS: Condition Zero), it was originally named Dust3, as ironically, Johnston was afraid that, since sequels are expected to improve on the original, this new map might fail in that regard.
As he settled to work on it, using elements from the original Dust, Dust3 gradually evolved into what we now know and love. When it was sent to Jess Cliffe, he said that it had to be renamed to Dust2.
And that’s how we got Dust2. Played by around 30,000 players at any time (which is 15% of all online gamers at any given time), it’s widely used by public servers to elite gaming leagues.
Johnston tweeted about it on that very day. There’s also a great making-of post on his site.