Written by Brian Stelter for the New York Times

Current TV said Friday afternoon that it had terminated the contract of its lead anchor, Keith Olbermann, scarcely a year after he was hired to reboot the fledgling channel in his progressive political image.

The cable channel indicated that he had failed to honor the terms of his five-year, $50 million contract, giving the channel the right to terminate it. Starting Friday night, the former New York Gov. Eliot L. Spitzer will take over Mr. Olbermann’s 8 p.m. time slot.

In a stream of Twitter messages, Mr. Olbermann responded to Current’s announcement by stating that “the claims against me in Current’s statement are untrue and will be proved so in the legal actions I will be filing against them presently.”

In a letter to viewers, the channel’s founders, Al Gore and Joel Hyatt, wrote: “We created Current to give voice to those Americans who refuse to rely on corporate-controlled media and are seeking an authentic progressive outlet. We are more committed to those goals today than ever before. Current was also founded on the values of respect, openness, collegiality, and loyalty to our viewers. Unfortunately these values are no longer reflected in our relationship with Keith Olbermann and we have ended it.”

Mr. Olbermann will not be given an opportunity to sign off, since Mr. Spitzer will start his new show, “Viewpoint With Eliot Spitzer,” on Friday night. This will be Mr. Spitzer’s second shot at an 8 p.m. talk show; in 2010, two years after he resigned the governorship after admitting to his involvement in a prostitution ring, he led a short-lived show on CNN. It was cancelled in mid-2011.

“We are confident that our viewers will be able to count on Governor Spitzer to deliver critical information on a daily basis,” Mr. Gore and Mr. Hyatt wrote.

With those words – “on a daily basis” – the founders of Current hinted at one of the reasons for Mr. Olbermann’s termination. It was the culmination, at least in part, of months of infighting between the famously temperamental Mr. Olbermann and his bosses at Current. He clashed early and often with Mr. Hyatt, and David Bohrman, the channel’s president, and it spilled out into public view in January after Mr. Olbermann declined Current’s requests to host special hours of election coverage, apparently out of frustration about technical difficulties that had plagued his 8 p.m. program, “Countdown.”

Lawyers interceded in the rift, and they appeared to work out an arrangement for future primary election nights.

But in January and February, Mr. Olbermann continued to miss many days of work, as he himself acknowledged on his Twitter feed. He attributed some of his absences to throat problems.

But Current considered some of those absences to be breaches of his contract, labeling them “unauthorized absences,” according to a person familiar with the matter, who insisted on anonymity because the executives involved had agreed not to comment on the record. For instance, he took a vacation day on March 5, on the eve of the Super Tuesday primaries, despite a warning from Current that it would constitute a breach of contract, according to the person.

On that same day, Mr. Hyatt stood by Mr. Olbermann in an interview with The New York Times, calling him unquestionably “the big gun in our lineup.” Referring to Current, Mr. Hyatt said, “it’s all on top of his shoulders.”

But behind the scenes, tensions were mounting and Current was quickly populating its schedule with new political programs, in part as a hedge against the possibility of Mr. Olbermann’s departure. The interview with Mr. Hyatt came on the day that Current announced two simulcasts of morning radio shows, effectively tripling its hours of live political talk each weekday.

It is unclear when the decision to dismiss Mr. Olbermann was made, but it was unanimous among the senior managers of Current, the person familiar with the matter said. A termination letter was sent to him on Thursday morning, and he did not appear on Current on Thursday night.

To many in the television business, the separation was a question not of if, but when. Mr. Olbermann has a history of abruptly and angrily leaving jobs, dating back at least to his days at ESPN, where he was a co-anchor of “SportsCenter” in the 1990s.

Fourteen months ago, Mr. Olbermann abruptly left MSNBC, where he had worked for the prior eight years. There, he nearly single handedly gave the channel an identity as a liberal counterweight to Fox News, but he also alienated staff members and crossed NBC executives by donating to Democratic politicians.

Executives at MSNBC had no public reaction on Friday to Mr. Olbermann’s departure from another channel.

In his forty weeks on Current TV, Mr. Olbermann had an average of 177,000 viewers at 8 p.m., down from the roughly one million that he had each night on MSNBC. Just 57,000 of those viewers on any given night were between the ages of 25 and 54, the coveted advertising demographic for cable news. Still, Mr. Olbermann ranked as the highest-rated program on Current, as Mr. Hyatt acknowledged earlier this month.

At that time, he called getting Mr. Olbermann a “programming coup” that “clarified the strategic direction we’re aggressively talking today.”