Gennady Tartakovsky was born in Moscow but moved to the US at age 7, at that point in his early life is where he was introduced to cartoons by watching Hanna Barbera cartoons, which is what most often aired on cartoon network, a few examples such as the flintstones, top cat, scooby doo and more. A style we recognize in Dexter’s laboratory, which started off with a short animation of dexter made while in university, that led him to be hired as a director for the show itself. 
Movieweb, Genndy Tartakovsky: every animated series ranked 2022.
“helped pioneer the Cartoon Network global domination of the 1990s with major input in both Dexter’s Laboratory and The Powerpuff Girls.”
“The Dexter character originally came out of an extremely impressive short that Tartakovsky had made in college – one strong enough for Cartoon network to commission a whole show on.”
Based on what was said, we already where his art style took great influence from, focusing on really exaggerating the shape study, very comical characters with exaggerations based on what message needs to be conveyed.
On an article by Esquire, we asked an animation legend about his five favourite cartoons
He mentioned a short animation by one of his favourite animators, Robert “Bobe” Cannon who worked on little rural riding hood (1949) he appreciated the exaggerated comical effect created as well as the simplicity of the characters. A style that stuck to him and is an element that should be kept in mind when trying to created characters in the hotel Transylvania setting through his style. This is an animation I had already seen and took some inspiration from the more beautiful looking red riding hood when I was stilling exploring the more pin up doll style of the 50s.( a different kind of exaggeration).
We also see and influence from comic books and anime:
Two anime’s of which he named as his favourites in Esquire for their story telling and character relationship rather then the style itself, (plot and story) being Laputa: castle in the sky (1986) which influenced him while working on Unicorn: Warriors Eternal (2023).
And CowBoy Bebop, the way the episodes were played out to vary each time inspired him for his future projects, and a little extra element I found amusing and something that shows how much of an importance to the world of animation he became (On a selfish note: one of the animators told me that he really liked Samurai Jack back in the day, and it helped influence them to make their next show, Samurai Champloo. That was amazing.”)(also from esquire)
(Although not American but maybe taking influence from there, it reminded me of comics I grew up with such as Lucky Luke by Belgian cartoonist Morris and Asterix and Obelix written by Rene Goscinny and illustrated Albert Uderzo both French.)
A side note:
knowing he came from a Russian background and lived there his early childhood, He might have not seen those old soviet era cartoons or perhaps he was too young to remember, but having grown with my mother side of the family as influence when it came to Russian cartoons during the soviet union. I recognise the comical look of some characters and at times the simplicity of characters, A short animation called Little Locomotive from Romaskovo (1967) The little girls reminded me of the powerpuff girls, it’s perhaps a stretch but it was fun remembering those old animations that fascinated me as a child. My mother also noted, because she is a big fan of samurai jack and used to watch it when it was airing on TV the sceneries reminded her of those landscapes also seen in the soviet era cartoons and wondered if the person behind it might have been from Russian origin. Not to be too repetitive, it might be a long stretch but it was a fun connection to make while exploring all the different cartoons he grew up with.
the notes:
To conclude:
Tartakovsky uses an emotion as a main base for the whole characters design ( sharp shapes, soft circle, posture, shapes, etc) as well as the shape study being a very prominent feature in the characters design. ( he mentions that in an interview with Techsupport, titled “Genndy Tartakovsky answers animation questions from twitter”). He also mentions often his love for the more old school times of animation in cartoons.
