Origin 

Groonk is some type of mutant that came into conflict with Thunderstrike when he was stealing gifts from civilians during the Christmas season. Eric Masterson was shopping for a Christmas gift for his son when a female shopper was taken into an alley by the Groonk. Masterson heard the lady scream and saw the Groonk running behind the building. Masterson transformed into Thunderstrike but lost the Groonk when he slipped under a manhole. Thunderstrike was patrolling the streets when the Groonk attacked another shopper. Thunderstrike and the Groonk engaged each other and the fight ended up inside a store. Groonk punched Thunderstrike into the escalator and ran off when a dog wearing reindeer antlers starting barking at him. Groonk grabbed the dog and headed into the tunnel systems below the streets. Thunderstrike followed his attacker and engaged him again. Groonk was laid out when a number of homeless individuals tried to bring down Thunderstrike. A young girl named Cindy Lou and her dog Max stepped in front of Thunderstrike and told him that Groonk was their friend. Cindy Lou and the other squatters told Thunderstrike that they found the Groonk wandering in the tunnels and he's usually gentle as a kitten. Cindy had read a Christmas book to the Groonk and in his own clumsy way, he was trying to provide gifts for the children. The squatters tried to teach Groonk what he was doing was wrong but he didn't understand. They promised to return the gifts as long as the Groonk stays with them and doesn't get arrested. Thunderstrike allows the Groonk to stay with his family and enjoy the holidays with them. 

Creation

The Groonk was created by Tom DeFalco and Ron Frenz in 1992 and first appeared in Thor # 444. He is inspired by the Dr Seuss creature the Grinch. 

Powers & Abilities

Groonk has superhuman strength, durability and resistance to injury. Groonk can also emit an energy blast from his eyes for range attacks. It is a potent attack, enough to even temporary weaken Thor.