Definition of "thanker"

He asked about six questions during my yarn, but every question had a point to it. At the end he bowed and thanked me once more. As a thanker he was main-truck high; I never see anybody so polite.

1913, Joseph C[rosby] Lincoln, chapter IV, in Mr. Pratt’s Patients, New York, N.Y., London: D[aniel] Appleton and Company