Sky News boss Nick Pollard, who resigned suddenly on Sunday after a decade in charge of the channel, has been described by one rival as "the most gifted TV journalist of his generation".
Pollard, who will be replaced by John Ryley, told staff his decision to leave the company after 10 years was based on a number of factors, but there is speculation he was under pressure following the channel's relaunch last October.
According to one industry source, Ryley was only offered the role of head of Sky News late last week and his succession was not a foregone conclusion.
Pollard's departure follows a year in which Sky News received praise for its coverage of the tsunami, the 7 July bombings and the Buncefield oil depot explosion.
But in October, Sky embarked on a major relaunch, breaking up its rolling news format for the first time since its launch 17 years earlier, with more "appointment to view" scheduled segments.
The appointment of Eamonn Holmes at that time has failed to make a significant impact on breakfast audience figures. Neither has an evening news show presented by James Rubin, former US president Clinton's former advisor.
In January, speaking at a Media Society debate on 24-hour news, Pollard admitted that the months following the channel's relaunch had been the "toughest time in Sky News's history". He also said that the BBC's ability to invest in its rolling news operation "was always what Sky would have to fear —I am under no illusions".
David Mannion, editor-in-chief, ITV News, told Press Gazette: "Over the years, Nick has become a giant of British television news. He was, for many years, a quite brilliant programme editor of News at Ten at ITN, but more recently he has turned Sky News into a brand leader.
"His drive and energy are legendary, but he is also a thoughtful and highly intelligent journalist, whose influence at Sky will be sorely missed."
Dominic Crossley-Holland, former controller of current affairs, arts and religion at ITV, who also ran its 24-hour news channel, said: "John has a unique combination of being able to see the overview and being able to translate even the most challenging stories into exciting and authoritative television.
"A tough taskmaster, but very fair, John works phenomenally hard and cares deeply about what he does.
"He's an inspired news professional with a glint in his eye and — I'm sure he wouldn't mind me saying — a sartorial disaster zone."
Crossley-Holland referred to Pollard as the "most gifted TV journalist of his generation" and said that he had a genius for understanding and exploiting breaking news.
Ryley is not set to take over the role until September, and in the meantime Sky is sending him on a two-month course in business and finance at Wharton University in the US.
Ryley began his career as a graduate news trainee at the BBC and then moved to the BBC Nine O'Clock News.
He first met Pollard in 1989 when he joined ITN. When Pollard moved to Sky in 1996, Ryley went with him and became his ‘right-hand man' in the Sky News control and newsrooms.
Mark Calvert, who worked under Pollard as editor of Five News, said: "For 10 years, Nick has been an inspirational boss, a great mentor and friend. He has single-handedly driven the expansion of Sky News over the past decade.
"The great thing about Nick is, even though his management responsibility has increased over the years, he is still absolutely passionate and active in the newsroom when it comes to stories."