Grouchio Marxio is one of the three Marxio Brothers of Super Marxio World, an obvious parody of the Mario Bros.. Grouchio is depicted as the leader of the team, often belittling Chicio Marxio (and largely ignoring Harpio Marxio). Grouchio is also a play on Groucho Marx.
Grouchio is always dressed in the same attire - yellow shirt, red dungarees, a polka dot bow tie and a cigar. In his first appearance, the Marxios are seen as the leaders of the Casino Night Zone and it is on his orders that Chicio sends out the Trooper Badniks out to capture Sonic the Hedgehog and Porker Lewis. He also claims to be the one who thought of the rollercoaster trap designed to kill Sonic, but gives ownership back to Chicio when the plan fails.
In his first meeting with Knuckles the Echidna, Grouchio tries to shoot Knuckles with a sniper rifle but misses, promptly blaming it on Chicio. He then comes up with the plan to kill Knuckles on an uncompleted rollercoaster. Later, his quick thinking allows the citizens of Mobius to believe that Knuckles is simply part of an attraction, rather than fighting a hoarde of Badniks.
Along with the other brothers, he returned much later as the owner of the Chemical Plant Zone: they'd manage to convince Mobius that they'd been misled by Robotnik, and were given command of the Zone. They claim they're reformed and just want the Zone to be an efficient base of industry. They called in Sonic the Hedgehog to investigate a series of problems - revealed to be Megatox. While Sonic believed the Marxios had wanted him to be killed by Megatox, Grouchio denied this and it was left ambigious about whether he'd truly reformed.Much later after that, in Sonic the Comic Online, Grouchio was questioned by Sonic as to how a terrorist had obtained Mega Mack, a chemical only found in his Zone. Grouchio again claimed to be behind Sonic, and pointed him towards The Family. Most recently, Grouchio was seen leading the Zone's fight in The Battle For Mobius, ordering warriors Sab and Sol Furic to prepare Chicio's "Marxio Kart".