Baby Doll was a villain first featured in the Batman: The Animated Series episode of the same name. After her first appearance, she was used a few times in other BTAS episodes (most predominately in the episode "Love is a Croc"), but has yet to make a major appearance in any of the comics or other Batman media.
Mary Louise Dahl was an actress who was born with systemic hypoplasia, a rare condition which kept her from ever aging, meaning that she spent all of her life looking like a little girl. She became famous for a brief period when she played the title character in the TV sitcom Love That Baby (when she was 20, though she still looked like she was 3). She and the show were wildly popular, but as the series got older, the ratings dwindled. In the final season, the producers of the show decided to add a new character — Baby Doll's cousin who was called Spunky. Baby Doll was angry at Spunky because she thought that he was stealing her spotlight — especially on one occasion on her birthday episode, where she got her face planted into her birthday cake by him. Furious, she quit the show in order to turn herself into a proper dramatic actress.
Her first role other than Baby Doll was in Macbeth. Unfortunately, the reviews for the play and her acting were terrible, ruining Mary's chances of becoming a popular actress. When her career went down the toilet, she tried to get Love That Baby back on the air because it had been canceled when she left, but the networks turned her down. After that, Mary tried to get any job that came her way, but was always turned down due to type casting and her condition.
Without any jobs coming her way, Mary went through a rough, depressing period of her life where she realized that the only time when she had been truly happy was when she was in the show as Baby Doll, when she used to have a "family" in the show and was adored by millions of viewers.
Keeping her stage name as Baby Doll permanently, Baby went around with her hired goons and kidnapped all of the original cast of Baby Doll, bringing them together so that she get revenge on Spunky and have her old family back. She tied up all of the actors in the Baby Doll set and bought along the same birthday cake. After pushing Spunky's head into the cake, she then got a stick of dynamite, put it on the cake like a candle and lit it, planning to kill Spunky.
Spunky ruined her plan by grabbing the dynamite with his mouth and throwing it to the other end of the studio, throwing it far enough away that it exploded without hurting anybody.
Batman crashed into the room and revealed that the actor who played Spunky wasn't the actor but was actually Robin in disguise. After Batman and Robin had realized what Baby Doll was doing, they had gone to the actor, told him what was going to happen and the man had let Robin take his identity. When Robin had been captured, he had sent a radio signal to Batman who had traced it and found out where Baby Doll was hiding.
While Robin released the captives, Batman chased Baby into a nearby fair, and then into a Fun House. Inside the Fun House, Baby came across a hall of mirrors. Within one of the distorted mirrors, Baby saw herself as an adult — how she believed she should look without her condition. Knowing this to be fake, just as her family and life, she shot and broke all of the mirrors before breaking down mentally and running out of bullets. When the Batman walked up to her, she went peacefully, uttering her infamous catchphrase "I didn't mean to."
The next time we see her in a substantial role, it's a few years later. She got a job as a manager/concierge of a hotel but is frequently made fun of due to her condition and her history of her character and a criminal. Feeling like an outcast, she sees a news report about Killer Croc and identifies with him because he too is an outcast due to a medical condition. She helps him escape from prison and the two form a criminal duo: Baby Doll as the brain, and Croc as the brawn.
While Baby clearly adored Croc, it seemed that he only felt a casual fondness for her at best, and Baby found out that Killer Croc was cheating on her with random hussies, using stolen money to buy their affections. Enraged, she planned to kill both Croc and herself along with the city by causing an explosion in a power plant, so that they could be "together forever" in their next robbery. While it seems that they're doomed, Batman and Batgirl come crashing in to stop them. Croc, angry at Baby Doll, tried to kill her and gained the upper hand and started a fight with her and Batman. During the fight, Croc was injured and left unconscious by a blast of boiling hot water shot out of a pipe he had torn from the wall as a weapon. Baby felt sorry for Croc and yet again goes peacefully when Batman came up to her, saying "We could have lived happily ever after, just like in TV."
Due to a rare medical condition that Baby Doll has, she looks like a toddler, even though she is actually over 30 years old. In her first TV appearance, she wore the same costume that she wore in her TV series "Baby Doll" and talks in both her adult and little girl voice, depending on which voice is the most relevant to the situation. She carried an old rag doll of hers called "Mr. Happy Head" which contained a hidden gun, with the end of the barrel disguised as one of his eyes. She wore a light purple dress with dark purple buttons and a Peter Pan collar, white frilly socks and panties, black Mary Jane shoes, had blonde hair tied in pigtails with ringlet curls with dark purple hairbows and had light blue eyes.
When Batman: The Animated Series was revamped, many characters were redesigned, as was Baby Doll.
In her new form, Baby Doll still looked like a 3 year old, but now wore a pink dress. Her eyes were now black, her hair was made simpler and her hair color was a lighter shade of blonde (just at the beginning was with the previous series hairstyle) and wore black lipstick.
- Baby Dolls' first appearance is similar to that of Elmyra from Tiny Toons Adventures, with golden hair similar to that of Shirley Temple's as a child actor. Even their personalities are sort of similar in terms of being egotistical and wanting everything for themselves, not distinguishing between good and evil (at first).
- The character model for Adult Cousin Spunky was later reused in the Superman: The Animated Series episode 'Maxima', where upon arriving on Earth, Maxima is harassed by a group of men, one of which is Spunky.
- Baby Doll is one of three villains whose voice actors changed between the two series, the other two being the Scarecrow and Killer Croc.
- In an episode of Batman: The Brave and The Bold, "Invasion of the Secret Santas!" the villain Fun Haus is seen holding a doll with an appearance similar to Baby Doll. This doll turns out to be a bomb used against Batman and Red Tornado, but the latter elevates it before it explodes.
- Baby Doll made a brief cameo alongside fellow BTAS villain Roxy Rocket in the Elseworlds story Batman: White Knight where she still appears to be in a relationship with Killer Croc.
- In Baby Doll's first appearance of Batman: The Animated Series , her two male henchmen are modeled after Willy Gilligan and Capt. Jonas "The Skipper" Grumby of the classic sixties sitcom, Gilligan's Island.