While Cortana is embedded into the Windows 10 operating system and is available on smartphones, tablets and smart speakers, the assistant remains less popular than Apple's Siri and drives fewer specialty device sales than Amazon's Alexa or Alphabet's Google Assistant. But Soltero was a rising star inside Microsoft who was plucked up in Satya Nadella's first year as CEO.
The departure was announced to employees this week, according to ZDNet. Soltero's last day will probably be in December, according to a person familiar with the move. It's not clear what he'll do next.
Soltero tweeted about his departure after the ZDNet report.
"We are grateful for Javier's impact and strategic leadership over the last four years at Microsoft, and wish him well as he returns to his entrepreneurial roots," a Microsoft spokeswoman told CNBC in an email. "Bringing together all of our work in natural language, intelligence and assistance -- including Cortana -- enables us to innovate faster for developers, partners and customers."