rule with an iron rod

To rule, govern, or control a group or population with complete, typically tyrannical authority over all aspects of life, work, etc. A noun or pronoun can be used between "rule" and "with." He rules with an iron rod, and moves swiftly to gain control over any entity that is not already in his grasp. She has ruled this company with an iron rod for three decades, and it's going to be difficult for her to let go of control.

Stern or tyrannical rule. This term comes from Tyndall’s translation of the Bible (1526): “And he shall rule them with a rodde of yron.” It was later transferred to any kind of stern domination, either serious or ironic. For the latter, Anthony Trollope used it in Barchester Towers (1857): “In matters domestic she . . . ruled with a rod of iron.” See also iron hand (in a velvet glove).