Mexican-born Spanish dramatist of the colonial era who was the principal dramatist of early 17th-century Spain after Lope de Vega (Vega, Lope de) and Tirso de Molina.

Born into a prosperous family in Mexico, Ruiz de Alarcón went to Spain in 1600 to study at the University of Salamanca, from which he graduated in about 1602. After studying further at the University of Mexico, he settled permanently in Spain in about 1611 and held several government posts, being appointed to the Council for the Indies in 1626. He wrote plays for his own enjoyment rather than for financial reward.

Less prolific than his contemporaries, Ruiz de Alarcón wrote about 25 plays, most of which were published in two separate volumes in 1628 and 1634, respectively. His plays are notable for their superb plot construction, psychological subtlety, and ethical teachings. Most of his comedies of life in Madrid centre on a defect in a person's character: La verdad sospechosa (“The Suspicious Truth”) is a study of inveterate lying; Las paredes oyen (“The Walls Have Ears”) concerns slander; La prueba de las promesas (“The Proof of the Promises”) is an attack on ingratitude; Mudarse por mejorarse (“To Change Oneself to Improve Oneself”) inveighs against the fickleness of lovers. A skinny hunchback, Ruiz de Alarcón and his deformities were mercilessly ridiculed by rival dramatists, especially Lope de Vega.