Whether you’re playing it on your desktop, iPhone or iPad, we live in a world where just about everybody has played Plants vs. Zombies. But what if the zombies weren’t zombies at all? What if they were aliens?

Ars Technica writer Michael Thompson has posted up the secret history of Plants vs. Zombies. Thompson talks with series creator George Fan, who sheds light on the game’s origins as a sequel to Insaniquarium – a game which featured aliens terrorizing fish – and how it transformed into the finished product we know today.

“We knew we wanted to significantly change up the gameplay for the sequel,” Fan said, “and [we were] leaning toward it to being more defense-oriented than the first Insaniquarium. During that time I was also playing a lot of tower defense games in Warcraft III, and realized that they had this innate appeal that made me think of fond childhood memories like building forts out of sofa cushions and watching Swiss Family Robinson. I really wanted to capture that appeal, and once I realized that plants and zombies made a much better theme for this game than fish and aliens, I shifted from creating a sequel into creating a whole new game.”

For the complete article, including a number of sketches made during the development process, check out Ars Technica.