Lisa Braeden is the Love Interest of Dean Winchester and she is the mother of Ben (and Dean is Ben's possible father). She was played by Cindy Sampson.
During Season 3, the Winchesters are at a town where Dean had been before, and he meets Lisa again, and its somewhat awkward. The last time they met they'd had a one night stand and Lisa got pregnant sometime afterwards, although its unclear if it was from Dean's fling or from another man. Lisa is shown to still fancy Dean because she has a son named Ben who looks and acts very like him.
Ben is kidnapped by a Changeling, and the monster puts its child (which looks like Ben) in replacement. Sam and Dean work out whats happening, and fight the Changeling, and kill it, killing its children, and returning the captive children. Ben leads the kids to break out.
Lisa comes back in season 5 where Dean is preparing to fight Lucifer. Sam makes Dean promise that when its over, and when Sam is either dead or in Hell, Dean will go back to Lisa and live a normal life with her and Ben. Dean eventually does so when Sam throws himself and Lucifer and Michael into Hell.
Lisa has the biggest appearances in season 6. Dean has spent a year living as a husband and wife with Lisa as promised. However, things go bad when Djinn attack. Dean kills the Djinn and meets Sam, alive. This surprises Dean and he asks how long he'd been out of Hell without telling him. Sam seems odd, and Dean is worried he is still possessed by Lucifer, he calls Castiel, but Castiel confirms Sam isn't possessed. Dean still has sex with Lisa occasionally.
One day, sometime later when Lisa has a new boyfriend, demons break into the house and kidnap Lisa, killing her boyfriend, and Crowley comes after Ben. Crowley calls Dean to tell him to rescue Lisa or he'll kill her and Ben. Crowley however has a demon possess Lisa, and this almost succeeds in killing Dean until the demon impales Lisa with her knife and she is mortally wounded. The demon flees.
In hospital, Lisa is slowly recovering, and Ben is with her. Dean asks Castiel to erase Lisa and Ben's memories of him and Sam because of the trauma it ended up n. So Castiel does so and when Lisa recovers, she greets Dean with a pleasant smile, forgetting all about him.