Galileo, often called "Galli" by the other characters, is an astronomer residing in the peculiar town of Galihabara and serves as one of its most energetic residents. His character is directly inspired by the historical scientist Galileo Galilei, a nod reflected in his name, his passion for astronomy, and his unwavering support for the heliocentric model of the solar system. This connection is visually represented by the T-shirt he always wears, which bears the phrase "Heliocentric Snow".

In terms of physical appearance, Galileo typically presents a short, stocky, and somewhat comical figure with a three-head body proportion. However, he possesses the remarkable ability to transform, when he wishes, into a tall, handsome man with an eight-head body ratio. He makes his home in a room at a boarding house run by Madame Curie, though he also frequently carries out his astronomical work at a local observatory.

Personality-wise, Galileo is the primary source of comic relief in the series. He is an enthusiastic and well-meaning scientist, but his demeanor is often clumsy, overly dramatic, and painfully unaware of how others perceive him. He fancies himself a groundbreaking discoverer, but the other residents and even newcomers to Galihabara rarely take him seriously. This leads to him being the frequent target of physical gags, enduring regular beatings from Madame Curie or being sent flying, rolling, and exploding, yet he somehow always bounces back. Despite his role as a mentor figure to the main character, Marika, she often pays him little attention, particularly when she first arrives. He is nevertheless persistent in his attempts to teach, using humor and relatable scenarios to explain scientific principles.

His key relationships are defined by rivalry and friendly antagonism. He shares a competitive dynamic with Leonardo da Vinci, often squabbling with him, though he is frequently on the losing end of these exchanges. He is also shown to be a rival of sorts to Isaac Newton. In a running gag for the series, his many misfortunes at the hands of other characters make him a classic "butt monkey".

Galileo's role in the story is central as the initial guide and science enthusiast who tries to spark an interest in science in Marika, a girl who initially hates the subject. His methods are unconventional and his lessons often go awry, but his dedication to showing the wonder of discovery is a driving force for the narrative. Over the course of the series, he remains a consistent, if chaotic, mentor figure. A notable moment in the second season shows a different side to him when he falls for an older, grown-up version of the new protagonist, Norika, hinting at a capacity for unexpected romantic feelings.

Galileo's notable abilities are as comical as his personality. Aside from his skill in astronomy and the physical transformation he can undergo, he has a high tolerance for pain, surviving constant physical abuse and slapstick violence. He has also been known to invent gadgets, such as a "universal skateboard," demonstrating a hands-on approach to science. Above all, his greatest ability is his unwavering and infectious enthusiasm for science, which he channels into his unorthodox attempts at teaching, helping demystify complex topics through action and exaggerated examples.