Rule the roost
Definition 1 of 1
Pro Tip 1/3Authority Figure
Used when someone has the final decision-making power, often in a family or small group. 
At family reunions, my grandmother always rules the roost.
Pro Tip 2/3Informal Setting
Mostly used in casual conversation, not in formal or business environments. 
During the team outing, it seemed like the interns ruled the roost.
Pro Tip 3/3Light Humor
Often carries a humorous or light-hearted tone, especially when power is unexpected. 
Despite the new manager, it’s the office cat that really rules the roost.