(Old fashioned) King-like position that enjoys using their power over others. Act as the authority or controlling figure. As a middle ages lord of the manor could command  his minions, so this phrase implies that someone has full control over your work or even lifestyle.  (Compare to Head honcho, Heavy handed, Call the shots or Rule the roost.)

“Since he got promoted to vice president,  he has been lording over everyone else in the office as if  he’s more important.”