William Hanna and Joseph Barbera originally had the cat named Jasper and the mouse was Jinx, in 1940's Un gatto messo alla porta (1940) cartoon. This is the first cartoon with their names, Tom Cat and Jerry Mouse.
The first "official" Tom and Jerry cartoon ever. The first one that was Un gatto messo alla porta (1940).
This is the first Tom and Jerry cartoon to use a 1941-1943 opening titles.
This is the first Tom and Jerry cartoon to be animated by Irven Spence, Cecil Surry and Bill Littlejohn.
In the script, the cat's name was "Jasper". By the time Lillian Randolph did the voice track as "Mammy Two-Shoes", the cat's name had been changed to "Thomas".