In 2003, the agency’s investment arm, DARPA, tapped the non-profit research institute SRI International to lead a five-year, 500-person effort to build a virtual assistant, one the government hoped might yield software to help military commanders with both information overload and office chores. Although it wasn’t the project’s mission, this helper, the Cognitive Assistant that Learns and Organizes, or CALO, would ultimately provide the inspiration and model for Siri.

Lots of stuff you might not know about Siri’s origins in this Huffington Post piece.