Apple

From KeenWiki

Apples (sometimes also called Apels) are apelike creatures (in that they walk on their knuckles) found in Apple Acres in Tuberia in Keen Dreams. They can climb up and down poles and will follow Keen if they can, hoping to knock him off as they climb much faster than he does.

The spelling of the name is somewhat of a mystery, as the creatures themselves are frequently referred to as Apels, but the name of the level most of them are found in is called Apple Acres.