In his “Market Structure and Equilibrium”, 1934, Stackelberg formulated a simple model about duopoly situations (a special case of oligopolies) known as Stackelberg asymmetric duopoly or more often simply just “Stackelberg model”
This model considers two players (firms): one is a leader, the other is a follower. Following a sequential game, the leader firm sets its production quantity and then the follower firm, after observing the leader’s behaviour, sets its own quantity. Both firms aim to maximize profits and their decision is on quantities rather than prices. The equilibrium reached (known as “Stackelberg equilibrium”) is the perfect equilibrium in this kind of games.