Palpatine was born on Naboo and was a member of the royal House Palpatine, of which his father was the patriarch. Ever since he was a young child he had considered himself superior and far more powerful than his father and his siblings, creating tension and hostilities within the family. He became fascinated with politics at an early age, aspiring to be politician for Naboo. As a child, he became obsessed with Sith history and collecting their ancient artifacts. He would use his family’s wealth to buy these artifacts from the black market. As a teenager he enjoyed racing on speeders, and eventually killed two pedestrians in a race. His parents used their wealth to help him, but he showed little remorse. He grew up to become a Republic Senator for Naboo, while discovering he was force sensitive.
Around this time he was approached by Darth Plagueis, one of the wisest Sith to ever live, and was offered a position as his apprentice. Being obsessed with Sith lore since a young age, Palpatine agreed and began training in secret while continuing his role as a senator. However, his final trial before becoming a Sith was to slaughter his entire family, which he happily did. While gaining popularity in the Senate, he trained in particular Sith skills involving manipulation such as mind-clouding. When he was appointed as an ambassador, Palpatine received an infant Dathomirian from the dark side cult known as the Night Sisters. This child was trained from an early age by Palpatine behind Plagueis’ back. This child would grow up to become Darth Maul. Gaining the trust of Queen Amydala, Palpatine was able to climb through the ranks easily. He lost many elections, but was so wealthy that he never stopped campaigning, leading to him being a popular political figure throughout the Republic. He eventually murdered his master in his sleep to take the role of Sith Lord. The fact that Palpatine didn’t confront Plagueis in battle shows how sly and cunning he was. He manipulated the Senate into granting him the title of Chancellor by the time he was an old man. This was the start of his ploy to cause a galactic civil war which would eventually destroy the Jedi and allow him to establish the first Galactic Empire.
To summarize it, Palpatine was always an evil and maniacal person even as a child. He wanted nothing but power and control and would do anything necessary to obtain it.