After Drupal was initially developed, thoughts turned to the creation of a logo. Of course the concept would have to include a drop, or water in general.
The initial idea was simple: a drop within a circle. It was conceived as an "O" in a fluid "drop".
Somewhat later there was an idea to use a cartoon-like drop with a face. Steven Wittens (UnConeD) created a 3D version, but the idea didn't get too far, mainly because 3D is difficult to work with.
When the logo issue came up again, Kristjan Jansen (Kika) came up with the idea of putting two sideways drops together to form an infinity symbol. When placed inside a filled circle, it resembled a face. After more work by Steven Wittens, the Druplicon was created: a stylised drop with the "infinity" eyes, a round nose and a mischievous smile.
You can find more versions of the logo in the marketing section.