If the melancholy Jaques is a glass-half-empty kind of guy, then Duke Senior is the play's glass-half-full character. The first time we meet him in the Forest of Arden, he's living in exile because his little brother (Frederick) has stolen his dukedom.
Despite the fact that he's been betrayed by his own brother and now lives in a cave, Duke Senior doesn't let anything get him down. He tells us that, even though Arden is cold, windy, and rugged, it seems like the Garden of Eden to him because, in Arden, he finds "books in the running brooks,/ Sermons in the stones, and good in everything" (2.1.1).
Still, Duke Senior isn't just some philosophical guy hanging out in the woods and twiddling his thumbs. He's also kind of tough because he's managed to thrive in a forest where some other city-slickers (ahem, Adam and Orlando) nearly starve to death. What's more, he's established a little social community made up of his most loyal followers from court, who have willingly exiled themselves to be near him. At one point, Charles notes how "many merry men with him" in Arden "and there they live like/ the old Robin Hood of England" (1.1.3).
Because Duke Senior lives in exile with his crew, he's associated with the legendary English outlaw who stole from the rich and gave to the poor, flipping the bird to those in power every chance he got. When you think about it, Duke Senior does have a desperado thing going on. The fact that he's managed to make Arden work for him despite his lousy circumstances is a way of opposing his corrupt and powerful brother.