Caster's true identity is "Michelangelo di Lodovico Buonarroti Simoni," one of greatest artists and the greatest sculptor of his time, and a member of the High Renaissance's Trinity, alongside Leonardo da Vinci and Raphael.
As early as the age of six, Michelangelo developed a passionate love for marble, and taught himself the fundamentals of handling a chisel and hammer by making small figures. At the age of thirteen he became apprenticed to premiere artist Domenico Ghirlandaio, who possessed the largest workshop in Florence at the time. Within the following year he became a paid artist under him, as well as Ghirlandaio's star pupil. By the time he was eighteen, Michelangelo had already sculpted numerous masterpieces including the Madonna of the Steps, the Battle of the Centaurs, and a greater than life-sized sculpture of Hercules. By the time he was twenty-four, he had finished the Pietà. By twenty-six, he had taken on and finished the four decade old commision for the Statue of David. By this time, his name had already reached the furthest corner of artistic influence in Italy, having garnered the eyes of both the House of Medici and the Pope. Michelangelo had already become a legend.
Though, there was another artist whose reputation rivaled his own, and who he had little tolerance for. They called him the "dreamer." They called him the "True Renaissance Man." Personally, Michelangelo preferred the name "Horse-modeller" when referring to Leonardo da Vinci.
It's unknown exactly "why" the two held such a rivalry. It's contested that on their first meeting when Michelangelo was fourteen and studying sculpture at the Medici gardens, da Vinci had admonished the youth and his studies. Perhaps it stemmed from the time da Vinci criticized his contemporaries rendition of the the Battle of Cascina. It's also said that Michelangelo routinely insulted da Vinci for his procrastination (which Michelangelo himself won't deny). Though, onlookers would say the rivalry was quite one-sided, with the younger artist often being the instigator (again, which Michelangelo won't deny).
You could say that Michelangelo's antagonism stems from da Vinci's outlook and behavior. He was a free spirit who's disciplines extended far beyond art itself, and into the realms of science, mathematics, writing, inventing, magecraft, magic theory and so on. He was a person who took on many requests from patrons and friends, yet had to often be reminded of his promises, for his hobbies and myriad of half-realized dreams came before everything else.
Michelangelo was no such restless soul. He was always preoccupied with some prominent person's, house's or guild's commission, even when it meant his own projects had to be left at the wayside. How many years had he wasted in quarries, trying to gather marble for requests only to have them cancelled before the real work even began? How many sculptures and paintings were left unaccepted and then given away because their original commissioner changed their minds? How many roads did Michelangelo personally construct just so he could accomplish his work successfully?
Though they were both "Men of the Renaissance," they lived their lives as polar opposites. One as a man who, throughout his life, tried to realize as many of his dreams as possible, while the other a man whose life seemed dedicated to realizing the others' dreams.
...Hmm? Why does Michelangelo look so young despite his peak being around his early to mid-twenties? A good question. Perhaps it aligns with how a "certain someone" viewed him while they were still alive.
But really, who knows?