tower of strength - 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 dependable person on whom one can lean in time of trouble, as in After Dad died Grandma was a tower of strength for the whole family. This expression, first recorded in 1549, originally was used most often to refer to God and heaven, but Shakespeare had it differently in Richard III (5:3): “Besides, the King's name is a tower of strength.”