Orestes and Electra
As brother and sister, these two are a clear set-up for a foil. Both commit to the same action yet end up on completely opposite sides of the existential spectrum. Electra retreats into bad faith while Orestes embraces his freedom and all the anguish that goes with. Nowhere is the contrast between these two more stark than in Act III, where their opposing reactions to the furies exemplify the differences between them. While Acts I and II bring brother and sister together to explore their similarities, the play's conclusion splits them apart and exposes their polarity.