Complex sentence: Alex Kidd, a video game character, is a monkey-like boy with big ears in a red jumpsuit and was commonly regarded as Sega's mascot until Sonic the Hedgehog debuted in 1991.
Split into simpler sentences: Alex Kidd, a video game series based around the titular character, who is a monkey-like boy with big ears in a red jumpsuit. He was commonly regarded as Sega's mascot until Sonic the Hedgehog debuted in 1991.