The co-founder and CEO of Siri, the company behind the voice control feature of same name that was the signature feature of the iPhone 4S, has left Apple due to personal reasons, according to a report on AllThingsDigital.

Dag Kittlaus spun Siri out of the Stanford Research Institute at the end of 2007. After the company was acquired by Apple in 2010, he stayed on as part of the company's speech recognition team, helping ‘make the next big thing into a really big thing,' according to his LinkedIn profile.

Kittlaus' departure is reportedly due to his family being based in Chicago, and his desire to take time off and brainstorm new entrepreneurial ideas.