Dyskolos (Greek: Δύσκολος, pronounced [dýskolos], translated as The Grouch, The Misanthrope, The Curmudgeon, The Bad-tempered Man or Old Cantankerous) is an Ancient Greek comedy by Menander, the only one of his plays, and of the whole New Comedy, that has survived in nearly complete form. It was first presented at the Lenaian festival in Athens in 316 BCE, where it won Menander the first prize.

It was long known only through fragmentary quotations; but a papyrus manuscript of the nearly complete Dyskolos, dating to the 3rd century, was recovered in Egypt in 1952 and forms part of the Bodmer Papyri and Oxyrhynchus Papyri. The play was published in 1958 by Victor Martin.

The story of the play concerns a rich young nobleman, Sostratos, who falls in love at first sight with a village peasant girl and decides to marry her. Unfortunately, her father, Knemon, is reclusive, notoriously bad-tempered, and next to impossible to approach. Eventually, after winning over Knemon's stepson Gorgias, showing his own work ethic, and helping to rescue Knemon from the well he has absurdly fallen into, Sostratos wins Knemon over and receives his blessing to marry his daughter. Sostratos also persuades his own father, Kallippides, to bless the betrothal of his own daughter to Gorgias. At the end of the play, Knemon is dragged kicking and screaming by the other characters to join the party for his daughter's wedding. As explained in the prologue, the events of the play are secretly orchestrated by the god Pan who wishes to reward the religious piety of Knemon's daughter and force Knemon, against his will, to experience a redemption arc.

The Dyskolos inspired Molière, who knew only the theme of the play, as it had not yet been found, in his writing of The Misanthrope (1666).

The backdrop of the stage consists of three buildings: the house of Gorgias (a farmer who is the stepson of Knemon), a temple of Pan and the Nymphs, and the house of Knemon (the Bad-Tempered Man of the title). The action of the play takes place in the street in front of these buildings.

The god Pan comes out from his temple, and explains the background to the play. The scene is the village of Phyle (some 13 miles north-west of Athens). He says that in the house next door lives a bad-tempered and irritable old man, living with his daughter and an old servant-woman. He tells how Knemon married a widow who already had a son by her first husband, but his continual bad temper caused her to leave him and go to live with her son. Pan says that because the girl won his favour by honouring the nymphs in his temple, he caused a certain rich city boy (Sostratos), who was hunting and spotted Knemon's daughter honouring the nymphs, to fall in love with her.

Sostratos, a young Athenian man who is hunting in the forest, enters with his poor companion Chaireas. He tells Chaireas about his love for the girl, and that he has sent his slave Pyrrhias to talk with her father. Suddenly Pyrrhias comes in running, shouting that he is being chased by a madman who is throwing stones at him. He explains how, when he knocked on the door, the old woman had sent him to the orchard where Knemon was working, and Knemon had been furious and beaten him up. Chaireas says that poor farmers are often bad-tempered. He promises to come back the next day to talk to the girl's father when he has calmed down; then he departs. Sostratos says he suspects that Pyrrhias must have done something wrong, and he sends him home, saying he is going to wait for the girl's father.

Knemon now enters from his orchard, grumbling about trespassers. Sostratos addresses him and says that he is waiting for someone. Knemon answers him bad-temperedly and goes inside. Sostratos, who is shy, decides that he must fetch his father's cunning slave Getas to deal with the matter.