Clym Yeobright: played by Michael Fassbender, Clym gives up a business career in Paris to become a schoolmaster for poor kids on Egdon Heath, his birthplace. Assorted trials attack him, including failing eyesight and a not-exactly-smart choice of a bride.
Eustacia Vye: played by Natalie Dormer, Eustacia is a high-spirited, stubborn woman and the local beauty--though also reputed to be a witch. She marries Clym, hoping that he will take her to Paris, but carries on an affair with Damon Wildeve.
Thomasin (Tamsin) Yeobright: played by April Pearson, Tamsin is Clym's cousin, who lives with his mother. She marries Damon Wildeve, but ultimately ends up with Diggory Venn.
Diggory Venn: played by David Call, Diggory is a "reddleman", a seller of red chalk and a strange traveling man. He ultimately renounces his nomadic trade, becomes a dairyman, and settles down with Tamsin.
Damon Wildeve: played by Colin Farrell, Damon is a good-for-little innkeeper with a wandering eye. He marries Tamsin while still carrying on with Eustacia.
And that's how Diana casts it. All images pulled from Google and Wikipedia.