walking encyclopedia

A very knowledgeable person, as in Ask Rob—he's a walking encyclopedia of military history. A similar expression, a walking dictionary, was used by George Chapman in his poem “Tears of Peace” (c. 1600).

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.