In 1940, the first Tom and Jerry cartoon, "Puss Gets the Boot", was released. In this film, Tom was called "Jasper". Another character that was introuduced in this film was Tom's black owner, Mammy-Two-Shoes. This name was tooken off earlier Disney model sheets and used for the ones of the T&Js, but she was never actually referred to that name in the cartoons. The original voice of her was almost always Lillian Randolph (Birdie the maid on the Gildersleeve radio show). There were a couple where she was unavailable, but the important one in all the Tom and Jerry classics was Lillian. She did other MGM cartoons too, not just Mammy-Two-Shoes. She also did similar roles for Disney in "Three Orphan Kittens" and "Figaro and Cleo".
The face of Mammy Two Shoes was deliberately hidden. We usually saw only the lower half of her body; the black maid's chin appeared once, as an exception, in "Part Time Pal", and the film's last shot showed Mammy Two Shoes far in the distance, pursuing Tom without our being able to see her feature clearly. Also in this short, it is revealed that Mammy wears a bandana (typical of black female cartoon characters of the 30's and 40's). We can also see (for a brief second) the back of her head when she "peeks in on 'dem two cats", before getting her butt slapped with a frying pan and shovel by Tom and Butch in "A Mouse in the House". We also see her complete body (but in a shadow) as she walks down the street (revealing she is wearing a hat with a flower) in "Mouse Cleaning". However, in 1950's "Saturday Evening Puss", we can see her whole body, including her face! Fred Quimby explained about this in an article published in a 1951 edition of The Hollywood Reporter:
"A young lady, after seeing a Tom and Jerry cartoon, inquired about the maid's face, which is never shown. To quote her (and we have it in writing lest there be any doubters among you): 'It gave me the impression that the operators in the booth must be having some sort of party, since every time the maid came on the screen, the only thing I could see was her feet. My curiosity is killing me. Before I go stark, raving mad, please tell me what she looks like.'
In this instance, we had an artist draw a special head of the maid to accompany the reply. We also explained that since Tom and Jerry were the stars of the pictures, we did not wish to do anything that might distract attention from them."
By the early 50's, Mammy was a supporting character just as important as Spike or Nibbles. However, in 1954, the Supreme Court declared racisism unconstitutional, which took a great affect on Hollywood movies and cartoons. So Mammy was forced to retire in 1952's "Push-Button Kitty". The new law pressured MGM to reissue the cartoons with her in them. The "White Mammy Two-Shoes" versions were created back in the 1960s for CBS when they were airing these cartoons. The work was done by Chuck Jones's crew when Jones was making new Tom and Jerry theatricals. I recall reading Chuck's remarks that at the time MGM still had most of its old animation artwork on file, so it was pretty much just a matter of retracing and repainting the original pencil animation and photographing it against recreated backgrounds. This new "White Mammy" material was then cut into dupe negatives of the cartoons in question to replace the original "Black Mammy" footage. Voice actress June Foray was brought in to redub the soundtracks. (Incidentally, that voice is supposed to be Irish.) Instances where the "White Mammy" has a "Black Mammy" voice (or vice versa) is a result of carelessness. Picture and sound elements on film masters are stored separately. What happens is simply that someone isn't paying attention and matches a newer "White Mammy" picture element to the original "Black Mammy" sound element (or vice versa).
Turner recently aqquired some redubbed prints which weren't quite as bad. Instead of a white woman providing her voice, they had another black woman provide the voice with less grammar mistakes. Recently, we've been seeing these "dubbed" prints air on CN (especially on late night showings). The following have recently aired dubbed: "Puss Gets the Boot", "The Midnight Snack", "Dog Trouble", "Puss n' Toots", "The Lonesome Mouse", "Old Rockin' Chair Tom", "Mouse Cleaning", "Polka Dot Puss", "Saturday Evening Puss", "The Framed Cat", and "Triplet Trouble". Dubbed versions of other cartoons, including "Part Time Pal" and "A Mouse in the House", have been said to have aired back a few years after Cartoon Network started. Hopefully in the near future, WB will release all of the Tom and Jerry cartoons uncut onto VHS or DVD, so everyone can see these treasures unedited.
Thanks to Keith Scott on information about the original voice. Thanks to The Censored Cartoons Page for much of the information on the dubbing.