rule with an iron hand

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 hand, and moves swiftly to gain control over any entity that is not already in his grasp. She has ruled this company with an iron hand for three decades, and it's going to be difficult for her to let go of control.

To rule with absolute firmness (concealed by a mild manner). Ruling with iron was an idea expressed in the Bible, in the Book of Revelation: “And he shall rule them with a rod of iron” (2:27). Iron hand in a velvet glove comes from Thomas Carlyle’s Latter-Day Pamphlets (1850) and is there ascribed to Napoleon Bonaparte: “‘Iron hand in a velvet glove,’ as Napoleon defined it.” However, the phrase has been attributed to other rulers, too, among them Charles V. Today it is more often used for lesser authorities, such as a strict parent, but may be dying out.

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).