What is the personality of Demetrius, and how does Shakespeare differentiate the young lovers?
Demetrius is stubborn and, one could say, full of himself. Demetrius is in love with Hermia, though she loves Lysander. Demetrius feels he has a right to Hermia, for her father has found favor in him, demanding that his daughter marry him. Demetrius does not take kindly to Hermia's preference and tries to sway them both to his claim, saying, "Relent, weet Hermia, and Lysander, yield/Thy crazed title to my certain right" (1.1.91-92)
Lysander is willing to help Hermia defy Athenian law and her father. He speaks with a lover's cooing words, for example, 2.2.47-48, in which he croons, "One turf shall serve as pillow for us both;/One hear, one bed, two bosoms, and one troth."
Demetrius (before the magic flower juice is applied to his eyes) is somewhat smug and self-righteous and has no sense of humour. When Lysander says to him, 'You have her father's love, let me have Hermia's. Do you marry him,' (quite a witty remark), Demetrius is outraged. As the chosen husband of Hermia he feels he has rights to her, and the fact that she does not want to marry him shows that he belongs firmly in the patriarchal beliefs of Hermia's father and the Duke of Athens, Theseus. He is less impulsive and ardent than the other suitor, Lysander. Of course, once he is bewitched by Oberon's messenger Puck, most of this changes.