Dorn is the local doctor and a friend of the family. He's fifty-five, handsome, well-educated and well-traveled. Women love him, and he loves them back. He flirts with Arkadina and Nina and carries on an affair with the farm manager's wife, Paulina. A bachelor by choice, he prefers to remain unattached. Paulina's entreaties for him to rescue her fall on disinterested ears; Dorn enjoys his freedom too much.
He's basically the Han Solo figure in this play. He's out for #1, but he's not a dirtbag about it.
In his physician's role as kindly but detached observer, Dorn often makes comments that reflect what Chekhov might say in a certain situation. Dorn's constantly singing relevant little songs. When Paulina nags him for his attraction to Arkadina, he good-naturedly admits it by singing "Once more, love, before you, enchanted I stand" (1.76).
Everyone loves actresses, he says, because "that's just the way people are. They're always looking for an ideal image" (1.76). And there Dorn has hit upon the core of The Seagull, the fruitless search to find an ideal image—a seagull, an approach to art, a lover—and to lock it down, to own it forever.
Dorn is alone (with the possible exception of Trigorin) in accepting the fleeting nature of life. He begs Sorin to accept his infirmity and to acknowledge his fear of death as an animal instinct. "You're sixty years old," he says, "Medicine won't help" (2.27). Dorn is philosophically inclined, as we see in his short but beautiful monologue in Act 4. Genoa is his favorite city in the world:
"Because of the crowds in the streets. Evenings, when you left your hotel, the entire street was full of people. You drift along with the crowd, no destination in mind, just back and forth; it becomes a living thing, and you become part of it, spiritually as well as physically; you begin to believe that a universal world soul is possible… like in your play, Konstantin, remember?" (4.65)
This big-picture view of the world creates a sympathy for Konstantin and his work. And despite his doctorial remove, Dorn really cares about the family. When Konstantin shoots himself, Dorn's first concern is protecting Arkadina.