opposite number, one's
One's counterpart, as in He's my opposite number in the California office. This expression is generally used for a person's equivalent in another organization or system (number alluding to their position in a hierarchy). [c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.