Mac Tonight was a mascot

Mascot

The term mascot – defined as a term for any person, animal, or object thought to bring luck – colloquially includes anything used to represent a group with a common public identity, such as a school, professional sports team, society, military unit, or brand name...

 introduced by McDonald's

McDonald's

McDonald's Corporation is the world's largest chain of hamburger fast food restaurants, serving around 64 million customers daily in 119 countries. Headquartered in the United States, the company began in 1940 as a barbecue restaurant operated by the eponymous Richard and Maurice McDonald; in 1948...

 restaurants in 1986. He was intended to advertise McDonald's late night hours to adults. He had a crescent moon for a head, wore a suit and sunglasses

Sunglasses

Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...

, and was depicted as being a jazzy lounge singer. The name was a play on words of the song "Mack the Knife

Mack the Knife

"Mack the Knife" or "The Ballad of Mack the Knife", originally "Die Moritat von Mackie Messer", is a song composed by Kurt Weill with lyrics by Bertolt Brecht for their music drama Die Dreigroschenoper, or, as it is known in English, The Threepenny Opera. It premiered in Berlin in 1928 at the...

", made popular in America

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 by Bobby Darin

Bobby Darin

Bobby Darin , born Walden Robert Cassotto, was an American singer, actor and musician.Darin performed in a range of music genres, including pop, rock, jazz, folk and country...

. The song that played over the advertisements, called "It's Mac Tonight", was also a variant on that song, but with McDonald's-themed lyrics, such as those featured in the original 1986 commercial:

"When the stars come out to play, babe

A twinkling show, ooh -- dinner! -- out of sight

Yeah, the night time is golden light time -- big dipper!

At McDonald's (showtime), it's Mac Tonight!"

Other lyrics include this set from a 1987 commercial:

"When the clock strikes half past 6, babe

Time to head for golden lights

It's a good time for the great taste -- dinner!

At McDonald's, it's Mac Tonight

Come on, make it Mac Tonight!"

Mac Tonight is the only character in the McDonald's world to not appear in the McDonaldland

McDonaldland

McDonaldland was a fantasy world used in the marketing for McDonald's restaurants. It was based on the "total concept and feel" of Sid and Marty Krofft's H.R. Pufnstuf television program. McDonaldland was inhabited by Ronald McDonald and other characters...

 advertisements.

It was known that Bobby Darin's daughter was not impressed with the song, due to the fact that she claimed that the song infringed upon her father's trademark, and that this was done without prior permission, and filed a law suit as well as an injunction for the song to be removed from both TV and radio ads.

Mac Tonight no longer appears in commercials in the United States, as a result of the injunction, but pictures of him can still be seen in some McDonald's

McDonald's

McDonald's Corporation is the world's largest chain of hamburger fast food restaurants, serving around 64 million customers daily in 119 countries. Headquartered in the United States, the company began in 1940 as a barbecue restaurant operated by the eponymous Richard and Maurice McDonald; in 1948...

 restaurants, and on some smaller signage by some restaurants' drive-through entrances/exits.
The campaign included 29 commercials, initially airing from 1986 to 1988.