In “As You Like It,” the exiled duke who lives in the forest is Duke Senior.
Duke Senior is the older brother of Duke Frederick, who has usurped his position and taken control of the court. After being banished, Duke Senior withdraws with loyal lords to the Forest of Arden. Although exile removes him from political power, the forest becomes a comparatively peaceful setting where his followers live freely and he develops a philosophical appreciation of nature.
Duke Senior is also Rosalind’s father. Rosalind remains at court for a time because Duke Frederick allows her to accompany his daughter, Celia. When Rosalind is later banished, she and Celia flee to the Forest of Arden, where Rosalind disguises herself as Ganymede and encounters Orlando.
The main confusion is between Duke Senior and Duke Frederick. Frederick is the younger, usurping brother who rules from the court; Senior is the displaced ruler living in the forest. By the end, Frederick undergoes a conversion and restores the dukedom to Duke Senior.