CBS Evening News with Walter Cronkite
Obviously, news had been done before 1962, when Walter Cronkite took over for Douglas Edwards, and it's certainly been done since, but it's hard to argue that it's ever been done better. Cronkite became the face of American information, and by doing so, personified the genre of TV news. What does a nightly news broadcast look like? It looks like the face that Cronkite gave it between 1962 and 1981.
During Cronkite's tenure, he was not only a conduit of information for events like Watergate and the Apollo 11 moon landing, but he also turned the nightly news into a vehicle that drove national policy -- and played a part in ending two presidencies. After Cronkite editorialized that Vietnam could at best end in stalemate, Lyndon Johnson bowed out of the 1968 presidential race. And after Cronkite's coverage of Watergate, combined with the famous Washington Post coverage, Nixon was finished.
By editorializing as well as reporting, did Cronkite blur the line between news and opinion? Is this misuse of his status as "the most trusted man in America"? Who knows. But it's certainly a model that's seen heavy use ever since.