VIDEO: MSNBC's Lawrence O'Donnell Pays Tribute to Keith Olbermann

In his first show since taking over the "Countdown" time slot, the "Last Word" host said "no one in television history has ever done anything like" what Olbermann did at the network.

Lawrence O'Donnell paid tribute to Keith Olbermann and his show's staff in his first episode since taking over the former Countdown host's time slot Monday night.

At the end of The Last Word, O'Donnell said he was impressed by the work that Olbermann, whose sudden departure from MSNBC was announced Friday, was able to do at the network over the past eight years.

"Consider what Keith invented and taught us to do: op-ed TV," O'Donnell said. "I marvel as any writer must at what Keith was doing. Five op-eds a week. Each of them much, much longer than the standard 800 words."

He also noted that the differences in the reaction to Olbermann exiting after eight years compared to when a long-running scripted show comes to an end.

"This is the only place in television where people are surprised if you leave after eight years," O'Donnell said. "In the entertainment division of this company, if a show like, say, The West Wing, wins every possible award and runs for seven year, everyone just applauds an extraordinary show for an extraordinary run. I saw exactly how exhausted the great Aaron Sorkin was after delivering 22 episodes a year of The West Wing. Well, Keith delivered 20 a month.

"I have no idea how he did it," O'Donnell added. "None of us do. No one in television history has ever done anything like it. No one knew it could be done before he did it, and in doing it, he took MSNBC to new heights."

O'Donnell , who frequently subbed for Olbermann in the host's absence, also reminisced about his first time filling in on Countdown, on July 27, 2009.

"I had never been nervous before doing television that night," O'Donnell said.

He went on to praise the show's staff -- many by name -- for giving him support and "confidence" back then.

"By the time the red light went on over my camera, I knew that I was in the hands of professional who simply were not going to let me fail," he said. "And when you saw me reading the TelePrompTer that July night, I know you were disappointed not to see Keith but you did not turn away, or I should say, click away.

"You keptwatching not because of me but because the same people who delivered you Countdown every night were still delivering you Countdown, the same people minus one, the most important one, but it was still Countdown."

O'Donnell went on to host several more times, including when Olbermann's father became ill and died.

"I know that I now occupy a platform built for me by Keith Olbermann," O'Donnell added. "Had he not built this show and welcomed me to it, I would be at home tonight watching, I don't know, the Real Housewives of somewhere."