Jack Dorsey Will Return As Twitter CEO

— -- Jack is back!

Jack Dorsey, 38, the former CEO of Twitter and one of the founders of the site, is taking over once again as chief executive, according to an announcement today from Twitter. Dorsey's appointment to his old position comes three months after Dick Costolo stepped down from the top job. Dorsey will also continue to serve as CEO of mobile payments company Square. Costolo, who served on the board during the transition process, is stepping down from the position today.

When Twitter's board began its search for a full-time CEO, it focused its search on finding someone who could devote all of their time to the position. After interviewing candidates and seeing Dorsey's success balancing his duties at Square and Twitter, it became apparent he was the right person for the job, said Peter Currie, who headed the search committee.

"Over time, it became clear to us that Jack was not only meeting but surpassing our expectations of him as interim C.E.O. while running Square," he said in a call this morning with investors.

Dorsey was previously chief executive of Twitter in its early days until co-founder Evan Williams replaced him in 2008. At that time, Dorsey took Williams' role as board chairman. With his return to Twitter, Dorsey will serve as chief executive while the board vets candidates for the chairman role.

While Dorsey wasn't initially expected to take over as permanent CEO, it was almost as if the entrepreneur was describing himself when he talked in a conference call with investors about what attributes the next CEO would need to have.

As a committee vetted internal and external candidates for the job, Dorsey said it was vital whoever takes the reins is "someone who uses and loves the product in every single way."

"Despite all we have accomplished, the company still has huge unmet potential," he said.

Stepping in full-time, Dorsey will be under immense pressure from investors to rise to that challenge. With more than 300 million monthly active users, Twitter has tremendous reach but has lagged in attracting and retaining new users, who in turn entice businesses to advertise on Twitter and drive revenue.

"The opportunity is absolutely massive. The intention is to certainly bring it to everyone around the world," Dorsey said this summer. "If we build a product people love and value, advertisers and users will follow."