What is the name of the character in The Great Gatsby known as 'the boarder'?

The character in The Great Gatsby known as “the boarder” is Ewing Klipspringer.

Klipspringer is a minor figure who spends so much time at Jay Gatsby’s mansion that Nick Carraway doubts he has any other home. He is not presented as a genuine friend of Gatsby, but as one of the many people who enjoy the millionaire’s hospitality and parties.

When Gatsby brings Daisy Buchanan and Nick into the mansion, they find Klipspringer in pajamas doing “liver exercises” on the floor. Gatsby then summons him to play the piano while Daisy and Gatsby reconnect. Klipspringer’s reluctant performance of popular music helps create the emotional atmosphere of the scene.

His behavior after Gatsby’s death reveals his shallow relationship with his host. When he telephones Nick, Nick initially thinks he may want to attend the funeral. Instead, Klipspringer asks Nick to send him a pair of tennis shoes he left at Gatsby’s house. That selfish detail reinforces Fitzgerald’s criticism of the empty social world surrounding Gatsby.