Berlioz is usually very quiet, but mischievous. He enjoys playing the piano, as seen when Duchess asks him to practice his Scales and Arpeggios with his sister Marie. He isn't easy to impress and can be annoyed rather quickly, usually he's the first to make a snide look or comment toward things he doesn't like. Still, he's shown to be just as naive and sweet-natured as his siblings.
Berlioz has blue eyes, dark grey fur (practically dark green fur) with a lighter stomach. He also wears a small red ribbon around his neck that is tied. Being a kitten, he's fairly small.
Berlioz first appears in The Aristocats during the opening credits, which display some of the scenes that he will appear in later.
Berlioz is next seen during the carriage ride during the beginning of the movie, where he rides on Frou-Frou's head. At the end of the carriage ride, his mother, Duchess, reminds him to thank Frou-Frou for letting him ride on her head (which he does). After asking how his thank you was, Duchess comments, "That was very nice."
Later, Berlioz is in a race with his siblings to see who goes through the front door first. When Marie states that she has the right of way, Berlioz sides with Toulouse's argument that Marie isn't a lady, even going as far to say that she is "nothing but a sister." Soon, Berlioz ends up in a fight with his sister (with Toulouse encouraging his brother from the sidelines). Berlioz tickle tortures Marie but ends up receiving punishment when his sister refuses to fight fair by tugging at his bow tie. Eventually, the fight ends when Toulouse accidentally knocks down a candle and it lands on Marie’s head. Duchess comes in to break up the fighting, insisting that fighting would not make them sophisticated (stating later that "Aristocrats do not practice biting and clawing and things like that"). Berlioz insists that Marie started it, while Marie retaliates, "Ladies do not start fights, but they can finish them!"
Soon enough, it is time for the family to concern themselves with self-improvement. While Toulouse goes to practice painting, Berlioz and Marie go to the piano to practice their music. Though there is a brief tiff between Berlioz and Marie when (thanks to Berlioz's piano-playing) Marie gets her tail squished, the fight ends and "Scales and Arpeggios" begins. Berlioz gets a little show-offish and, after Toulouse decides to join in on the playing, Berlioz and he end up in a piano battle that ends in a draw.
Later that evening he and his family are enjoying their dinner when they fall asleep. After a bump ride, he lands in a pond. He and his family later encounter Thomas for the first time. They go on a few adventures with him on a milk van and on a train bridge. Later the cats encounter Scat Cat and his friends and party.
A while later, they return to the mansion but their door is shut. They try to mew their way in but get captured by Edgar. The sack is sent into an old oven. He and his family get rescued by the musician cats and watch as a defeated Edgar is mailed to Timbuktu instead of them. He is seen getting a picture taken then running downstairs to join the party.
Berlioz, along with his brother Toulouse, oddly never appeared in "live" form at any of the Disney theme parks until February 2013, in Disneyland Paris for a Valentine's Day Event. He alongside Toulouse make occasionally meet and greet appearances at the resort.
Berlioz alongside Toulouse made their debut at Tokyo Disneyland in 2013 for the former daytime parade Happiness is Here Parade as part of the park's 30th Anniversary. Berlioz appears on The Aristocats float that's a giant piano along with Marie and Toulouse. Berlioz also makes meet and greet appearances at both Tokyo Disneyland and Tokyo DisneySea.
Berlioz shows up at Shanghai Disneyland for the park's daytime parade Mickey's Storybook Express alongside Marie and Toulouse. Berlioz along with the other kittens also appear at a daytime show near Fantasyland.
Berlioz alongside Toulouse also made their U.S. debut at Disneyland in mid-November 2019 as part of a Christmas Dance Party in Tomorrowland alongside Marie.
- Berlioz was named after a French romantic composer named Hector Berlioz.
- Berlioz resembles a younger version of Scat Cat. However, Scat Cat is grey with white patches around his eyes and nose, and Berlioz is completely grey, as noticed, they both wear the same red ribbons.
- Berlioz's Italian name is "Bizet", a reference to the musician/composer Georges Bizet.
- Berlioz is the only kitten whose name is not mentioned by Madame.
- Since Berlioz's sister Marie has his mother Duchess's white fur, and his brother Toulouse has Thomas's orange fur, it is possible that Berlioz's biological father had grey fur.
- Berlioz, alongside Toulouse, and Marie starred in a spinoff comic series "The Aristokittens" which ran from October 1971 till October 1975. The kittens encounter various Disney characters in the first two issues.
- Berlioz's name is only mentioned once by Marie and Toulouse.
- Berlioz, along with Marie and Toulouse, do not appear in House of Mouse.
- Berlioz is called "Berly" in the book instead of his real name.
- Berlioz is the only kitten whose name that's not mentioned a lot during the movie.
- Berlioz's name is never mentioned by Thomas O'Malley.
- Berlioz's name is pretty much only and always mentioned by Duchess.
- Berlioz is the only kitten whose ribbon that comes apart or untied.
- Berlioz is the first kitten to talk in the movie.
- Berlioz's talent is playing the piano and singing.
- Berlioz was going to be voiced by Nika Futterman in the sequel, The Aristocats II, known to be a female voice actress, even though he is a male kitten, replacing his original voice actor Dean Clark.
- Berlioz, Marie, and Toulouse don't have any friends as other kittens their ages.
- Berlioz is known to love playing violin besides piano seen in the canceled series The Aristocats: The Animated Series.
- Dean Clark who voices Berlioz only makes 1 film appearance, meaning Berlioz is the only character Dean Clark ever voices but doesn't make any other film appearances in other movies, not even himself in person.
- While Berlioz and Toulouse don't make an appearance in the Miriya & Marie manga. A new cat character introduced in the manga resembles Berlioz and serves as a male cat companion to a warlock who's Miriya and Marie's rival.
- Berlioz is the only kitten that doesn't call Thomas Mr. O'Malley.
- Berlioz says his final word "Aw, shut up, Toulouse." locked up in the oven, and doesn't talk again for the rest of the movie.
- Berlioz is the only kitten wearing a little ribbon, Marie and Toulouse's ribbons are bigger than his ribbon, so he's the only one that doesn't wear a big one like they do. However, there are a few scenes in the movie where his ribbon is a little bigger.
- Berlioz is the younger kitten and brother of Marie and Toulouse's, so this could lead to him being born second after Toulouse was born.
- Berlioz is the only kitten that doesn't talk very much in the movie.
- Berlioz says "Sissy Stuff" to Marie after she says "How romantic". Skippy also says that in Robin Hood.