Jack Dorsey is back at Twitter in a big way. He just tweeted that he is now taking on the lead product role at Twitter, the company he co-founded and where he’s remained as chairman. To reflect his new operating role, his title will now be executive chairman. Dorsey will remain CEO of Square.

News that Dorsey was negotiating with Twitter for an expanded role came out last week. There was some speculation that he might even take the CEO spot, but it is very difficult to be the CEO of two technology companies at the same time and Dorsey is “200%” committed to Square. All you have to do is watch this video to see how much he cares about building great products. And now he will be doing that at both Twitter and Square, while leaving the business side of Twitter to CEO Dick Costolo.

Dorsey stepped down from the CEO spot at Twitter in 2008, when he was replaced by Evan Williams. Williams subsequently handed over the CEO title to Dick Costolo, ostensibly so that he could focus on the product. But Williams supposedly hasn’t been around that much. When Williams stepped down, that opened the door for Dorsey to expand his role (there was some bad blood between the two), which is what’s happening now.

Twitter is now five years old. Dorsey recently put out some nostalgic Tweets about how the product got started. Today, Twitter is a different beast with more than 200 million users and an array of products (Web, mobile, tablets) that must be best-of-breed. Twitter began much more simply by providing the underlying service and encouraging other developers to build clients and features. The relationship with outside developers is now strained. Will Dorsey work to repair and reinvigorate those ties or focus more on making Twitter’s own products the only ones people need?

Today I'm thrilled to get back to work at @Twitter leading product as Executive Chairman. And yes: leading @Square forevermore as CEO. #200%—
Jack Dorsey (@jack) March 28, 2011

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Person: Jack Dorsey

Companies: Twitter, Square, Ustream, Thrive Capital, Fancy

Software engineer Jack Dorsey is the Co-Founder of Twitter, and was the CEO until October 2008. Dorsey had the original idea for Twitter while still at Odeo, a podcasting startup which was a project of Obvious Corp. He is now the chairman of Twitter. In May 2009, Dorsey announced his latest startup, Square. Square, originally code-named Squirrel, is a mobile payment startup with both an app and a piece of hardware that allows the iPhone and Android to...

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Company: Twitter

Website: twitter.com

Launch Date: March 21, 2006

Funding: $1.16B

Twitter, founded by Jack Dorsey, Biz Stone, and Evan Williams in March 2006 (launched publicly in July 2006), is a social networking and micro-blogging service that allows users to post their latest updates. An update is limited by 140 characters and can be posted through three methods: web form, text message, or instant message. The company has been busy adding features to the product like Gmail import and search. They recently launched a new site section called “Explore” for...

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Company: Square

Website: squareup.com

Launch Date: February 2009

Funding: $168M

Square is a revolutionary service that enables anyone to accept credit cards anywhere. Square offers an easy to use, free credit card reader that plugs into a phone or iPad. It’s simple to sign up. There are no extra equipment, complicated contracts, monthly fees or merchant account required. Co-founded by Jim McKelvey and Jack Dorsey in 2009, the company is headquartered in San Francisco with additional offices in Saint Louis and New York City.

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