iron hand (in a velvet glove), to rule with an

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.
See also: hand, iron, rule

iron hand (in a velvet glove), to rule with an

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.
See also: hand, iron, rule, velvet