MGM and its predecessor, Goldwyn Pictures, have been using a lion as its trademark logo since 1916. The practice continued when MGM was formed by the merger of Samuel Goldwyn's studio with Marcus Loew's Metro Pictures and Louis B. Mayer's company in 1924. Seven lions have been used in the logo's history. Although MGM has referred to all of the lions as Leo, only one animal was actually named Leo. He is the current one, which made his debut in 1957 (the same logo has been used for 60 years.)

The original lion was named Slats and was born in the Dublin Zoo. Slats was used in all black and white films made by the studio from 1924 to 1928.

The original logo, used from 1916 to 1924, was designed by studio publicist Howard Dietz. Dietz said he decided to use a lion as the company's mascot as a tribute to his alma mater Columbia University, whose athletic teams are called The Lions. The lion's roar was inspired by Columbia's fight song, "Roar, Lion, Roar".

Slats is the only lion that appeared in the logo that did not roar.

Slats died in 1936 and his hide is currently on display at the McPherson Museum in McPherson, Kansas.

The first lion to roar was named Jackie in 1928, in front of the film White Shadows in the South Seas. Jackie was also the lion in front of the Wizard of Oz.

Jackie also appeared in Tarzan films, photo shoots with movie stars and survived many accidents that earned him the nickname Leo the Lucky.

More Info: en.wikipedia.org