Siri co-creator Adam Cheyer has left Apple’s Siri Voice Unit reports Bloomberg. The co-founder is the second to leave Apple after Dag Kittlaus left post iPhone 4S release last year.

Bloomberg says that Cheyer is no longer working for Apple after having founded the Siri Voice Unit with Kittlaus after their “hiring” when Apple acquired their company back in April of 2010.

Kittlaus moved back to Chicago to be with his family after leaving Apple.

Apple CEO Tim Cook gave an interview at the All Things D conference earlier this year where he teased that Siri has “unbelievable potential”. “It’s one of the most popular features of our most popular phone. But there’s more that it can do,” said Cook “And we have a lot of people working on this. And I think you’ll be really pleased with some of the things that you’ll see in the coming months.”

At Apple’s WWDC event in June, Siri got a host of new features including sports score integration, movies, app launching and ‘Eyes Free’, a partnership with a bunch of big auto makers to extend hands-free functionality.

Now that Kittlaus and Cheyer have both left Apple, it’s up to other employees that made the jump to the Siri unit to shepherd its growth including, presumably, third founder Tom Gruber. There has been some grumbling about its accuracy and effectiveness, But Apple clearly continues to bet big on it as an information delivery service. It’s just one way in which Apple is working towards taking more control of the way that users retrieve information and perform actions on their devices, instead of out-sourcing those to Google.