The Frozen Fiend was the disguise of Galina Korzhakov, a Russian figure skater. She tried to scare people away by dressing as the Frozen Fiend so she could steal the priceless diamonds covering the Emperor's Cup.
According to Brett Hull, the ghost was supposedly once a Russian hockey player, who was banished to Siberia for not scoring the winning goal, and froze to death.
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The Fiend first appeared in the middle of a hockey game and it stole the trophy cup. Mystery Inc. decided to investigate, making them the Fiend's targets. After chasing them on an icy pond and at Lenin's Tomb, Fred Jones decided to catch it before the mystery had been solved. This didn't work out, and the Russian police arrested a framed Brett Hull.
When the gang saw through the plot, the Fiend went after them in a zamboni, which was stopped by something in the ice. Velma Dinkley realized they were the diamonds from the trophy cup and a trap was laid. When a bucket of water was dumped on it, the Frozen Fiend froze and was unmasked to be Galina. (Diamonds Are a Ghoul's Best Friend)