The term "announcer" is often used as an all-purpose description of a person whose voice is heard over radio or television.
I've heard people who more properly identified as newscasters or even actors referred to as announcers.
But people such as Don Pardo, who died this week, had specific duties which had more to do with their voices than their faces. If somehow you passed Pardo on the street, it's likely you wouldn't have recognized him. But if you heard him speak, you would have thought: "Where have I heard that voice before"?
Announcers on TV shows, as a rule, were heard more than seen. There have been exceptions to this. Both Johnny Olson and Rod Roddy had the role of announcer on The Price Is Right (as did Pardo in the show's early years), but they were often seen on camera, calling on newly-chosen contestants to "Come on Down!". Ed McMahon's role on Johnny Carson's Tonight show was as an announcer, but he was just as well-known as Carson's on-camera sidekick for nearly 30 years.
A more common example is Johnny Gilbert, who has been the announcer on Jeopardy! for the 30 years the syndicated Alex Trebek version has been on the air. (Pardo also was the announcer on that show's first version, in the 1960's and '70's.) When I saw a special taping of Jeopordy! in 2002 in Columbus, Ohio, Gilbert was seated at a lectern illuminated by a small reading lamp just off-stage; unglamorous as can be, introducing the host and doing some commercial voice-overs.
At one time, at TV stations across the country, announcers worked day-long shifts, usually doing live commercials and the legal station identifications ("this is WTAP-TV, Parkersburg-Marietta") that happen during local station breaks between network programs. Pardo did this at NBC's station in New York City, as well as occasionally for the network. The latter is why he was pressed into service to do the bulletin of the JFK shooting in Dallas on November 22, 1963, reading the same wire service bulletins local radio and TV people were reading across the country at that time.
As recordings gradually replaced live broadcasts on both radio and television, the need for live announcers diminished, along with the number of people employed for that purpose. So, in many ways, Pardo was among the last of a breed; someone who was not easily recognizable, but, in many ways just as welcome in our homes as those who were.