Chester the Interdimensional Imp was a fictional imp, in truth a persona constructed by Flintheart Glomgold.
In 2018, using a stolen Time-Teaser, Flintheart Glomgold resolved to try and drive his archnemesis Scrooge McDuck mad. As part of these operations, he disguised himself as a mischievous interdimensional imp by the name of Chester, and it is as Chester that he played various mean tricks on Scrooge using the Time-Teaser. He allowed Scrooge (but only ever Scrooge) to catch a few glimpses of “Chester”, so that he would sound even crazier to his family, raving about how it was an imp named Chester who was responsible for all his troubles. The Ducks nevertheless ended up figuring out that Glomgold was behind Scrooge's “illness” and tricking him into confessing his charade.