No list about Dexter would be complete without Arthur Mitchell (John Lithgow, who won an Emmy for his work). One of the biggest serial killers of all time (in Dexterland), he shows the future that Dexter could have. But it is how he murders Rita that irrevocably changes Dexter's life. After killing Mitchell, in the false lull of safety, Dexter waltzes home to find his son, Harrison, sitting in his dead mother's blood. This completes the cycle, back to Dexter's own beginnings of bathing in his butchered mother's blood, while forever altering the future. Long after "Dexter" ends, we'll always wonder if Harrison followed in his father's footsteps.