John Legere, the colorful CEO of T-Mobile who has amassed 6.5 million Twitter followers and is known for his "Slow Cooker Sunday" livestreams, will step down in 2020 after more than seven years at the helm, the wireless company said Monday.

Mike Sievert, T-Mobile's chief operating officer, will take over as chief executive in May. Legere said he will spend his remaining months as CEO focused on completing T-Mobile's merger with Sprint, a blockbuster $26 billion deal aimed at keeping pace with telecom rivals including AT&T and Verizon amid ongoing industry consolidation.

Sievert reiterated that goal Monday during a conference call with investors and analysts to discuss the change in leadership. "AT&T, Verizon and others will have no idea what's about to hit them and customers are going to be the winners," he said.

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As chief operating officer, Sievert heads all T-Mobile marketing and product teams as well as retail, sales and customer support staff. Sievert, a University of Pennsylvania graduate, previously worked as a senior vice president for Lenovo, a vice president for Windows marketing at Microsoft and an executive vice president for E*Trade.

Legere, who was named T-Mobile CEO in September 2012, said in the call that Sievert was one of his first hires and that it "has been exciting to watch him as he's taken more and more responsibilities, going from [chief marketing officer] to COO to president and COO and soon president and CEO and then, hell, who knows, maybe he'll become President."

‼️You’ve heard me joke that he’s “my son,” but in reality, since I hired him in 2012, @SievertMike’s been my mentee, my secret weapon and my friend. In our time we’ve launched 16 #uncarrier moves, shifted an archaic industry for consumers and wreaked havoc on the competition. pic.twitter.com/7MyX4i1vjd — John Legere (@JohnLegere) November 18, 2019

T-Mobile's board chairman, Tim Höttges, said in a statement that Sievert has the support of Legere and the "full confidence of the board."

T-Mobile for years has labeled itself the "un-carrier" wireless option, a moniker adopted during a 2013 marketing campaign in which the company eliminated annual service contracts, offered 4G speeds and stopped charging extra for using more than allotted data. Earlier this year, the company unveiled its Un-Carrier 1.0 program, which would give first-responders 10 years of free service, free wifi hot-spots to 10 million households that have troubled getting on the internet and 5G speed to customers.

"The un-carrier culture, which all our employees live every day, will not change," Sievert said.

Merger in the balance?

Un-Carrier 1.0 hinges on a successful Sprint merger. Both sides are still ironing out the details of the proposal, Legere said Monday, adding that there were shareholder meetings about the merger this past weekend.

"I don't have anything to announce, but there's certainly progress, there's been multiple discussions," he said.

T-Mobile and Sprint announced plans to merge in April 2018. However, attorneys general from 10 states including New York and Virginia filed a lawsuit in June to block the deal, arguing the merger would create only three major wireless providers and set the stage for higher prices. The case goes to trial December 9 in New York.

The Justice Department and the FCC approved the Sprint-T-Mobile merger earlier this year.

Analysts with New Street Research said there could be "tremendous value creation if T-Mobile acquires Sprint."

"We expect T-Mobile's current path to continue under Sievert [and] we suspect he has played a strong role in shaping T-Mobile's strategy for years," the analysts wrote. "We doubt the management change will materially impact the prospects for the case at trial."

Legere, who will remain on T-Mobile's board after his contract ends April 30, said he has had positive talks with state officials about what the merger could mean for customers and T-Mobile employees.

"I've actually had some fascinating dialogue in the last week with heads of labor who are learning more about the jobs picture here and seeing if there's ways for us to build bridges," he said.

Legere also shot down a report that he has talked to WeWork executives about taking over CEO of the struggling office space-sharing company. "I was never having discussions to run WeWork," he said in the call.