Twitter is getting the band back together.
"There's something about the personality of a company that comes from the folks who start it", Biz Stone wrote in a Tuesday Medium post.
"My top focus will be to guide the company culture, that energy, that feeling", he wrote in a Medium post.
Since leaving Twitter in 2011, Stone has kept busy with several entrepreneurial projects.
Mr. Stone admitted that at the time, he was overcome with emotion and realized that Twitter was the most important work of his life. "[Evan Williams] said it best when I told him about this turn of events, 'Well, you're among the best in the world at being Biz Stone'".
"Excited to have Biz's energy and heart back at Twitter!"
Stone's announcement is a vote of confidence in Dorsey and Twitter at a time when executives and some longtime investors are jumping ship.
Last month, Ev Williams, another Twitter co-founder, announced plans to sell as much as 30 percent of his stake in the company to fund other investments, but remains a member of its board. The company's stock rallied when Twitter's earnings this quarter beat analyst projections after previously sliding when it became apparent that a sale was not imminent.
Biz and Jack have maintained a close relationship since founding the company and also since Biz left, with regular catch up's in San Francisco and maintaining a close friendship. In April, the tech firm reported its first revenue decline since it went public in 2013. "I'll shape the experience internally so it's also felt outside the company", Stone said, promising to reveal "more soon".
In March, visual bookmarking site Pinterest said that it was acquiring Stone's company for an undisclosed amount. "I'm so lucky that I get to step back in and help shape it's [sic] future".