Definition of "impersonating"

"I don't want to get down on the floor," he said feebly; "is it necessary?" ¶ But they had already discovered that he could be bullied, and they had it their own way; and presently Selwyn lay prone upon the nursery floor, impersonating a ladrone while pleasant shivers chased themselves over Drina, whom he was stalking.

1907 August, Robert W[illiam] Chambers, chapter I, in The Younger Set, New York, N.Y.: D. Appleton & Company