walking encyclopedia - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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).