Twitter co-founder Jack Dorsey is returning to the company as an executive chairman.
Dick Costolo, Twitter's chief operating officer, made the announcement via Twitter on Monday. Dorsey had served as Twitter's CEO until 2008, when Evan Williams assumed the chief executive role. Williams stepped down last November, and Costolo stepped in as a temporary replacement.
Dorsey, currently the CEO of mobile payments service Square, will retain that title as well.
"Today I'm thrilled to get back to work at @Twitter leading product as Executive Chairman," Dorsey wrote. "And yes: leading @Square forevermore as CEO. #200%."
For Twitter, he will assume the role of chief product officer, with day-to-day oversight of all Twitter products.
The company recently celebrated its fifth anniversary. The service now averages 140 million tweets per day -- one per character! -- up from roughly an average of 50 million a year ago. (About 177 million tweets were published on March 11, the day of the earthquake and tsunami in Japan.) There are also more than 400 full-time employees currently working at Twitter.
