King Acorn (voiced by Tim Curry) was once the ruler of what used to be the great city of Mobotropolis, before Dr. Robotnik took over. It all started ten years ago, when the city was at war with an army from another land. The king discovered a human man named Julian Kintobor who showed promise. He appointed him warlord of the royal army. When Julian led his troops to victory. The king announced that he would hold a reception banquet and appoint Julian as the new Minister of Science. Little did the king know that Julian had plans of his own. After a certain time-travelling blue hedgehog and the future version of his daughter arrived at the palace to warn the king of the events that would change everything, it was too late. Juilan, now known as Robotnik, entered the palace, with his nephew Snively and army of SWATbots, and announced his takeover. The king was later captured and was thrown into the Void. There, he met the evil wizard Ixis Naugus, who wanted revenge against Robotnik for trapping him in the void. Ten years later, Sonic went into the void and rescued the king. But the reunion with Sally was short-lived, as he and Naugus were starting to crystalize, since they spent too long in the void. The king gave Sally a disk containing info on other Freedom Fighter groups. The king and Naugus went back into the void to reverse the crystalization process and the portal closed.
King Acorn's first and last names were never revealed in the animated series, but in the comic book series. If the series wasn't cancelled, The king would've been out of the void with Robotnik and Naugus.