strong silent type
A man of action who is reserved and masks his feelings. For example, Paula always preferred the strong silent type to more extroverted men. Almost never used for a woman, this expression may be obsolescent. [c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.