in one's element
In an environment naturally suited to or associated with one; doing what one enjoys. For example, He's in his element when he's doing woodworking. This term alludes to one's natural abode, as does the antonym, out of one's element (used by Daniel Defoe in Robinson Crusoe, 1719: "When they came to make boards ... they were quite out of their element"). [Late 1500s] Also see in one's glory.