The famous Superman line is
It's a bird, it's a plane, no it's Superman!
Who was the first person to say that in a Superman story?
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In 1941 and 1942, Fleischer Studios produced a series of seventeen animated shorts featuring Superman for Paramount Pictures. (Fleischer produced the first eight as an independent company before being acquired by Paramount in 1942).
Look! Up in the sky! It's a bird! It's a plane! It's SUP-er-man!"
is used as the introductory sequence for the very first one, called "The Mad Scientist". The "speakers" are random people in the street. The titles contain a caption
COPYRIGHT MCMXLI Paramount Pictures, Inc.