Diego Laynez (or Laínez) (Spanish: Diego Laynez), born in 1512 (Almazán, Spain) and died the 19 January 1565 (Rome), was a Spanish Jesuit priest and theologian, and the 2nd Superior General of the Society of Jesus.
Diego Laynez was born in Almazán in Castile. He graduated from the University of Alcalá, and then continued his studies in Paris, where he came under the influence of Ignatius of Loyola. He was one of the seven men who, with Loyola, formed the original group of Friends in the Lord, later Society of Jesus, taking, in the Montmartre church, the vows of personal poverty and chastity in the footsteps of Christ, and committing themselves to going to Jerusalem.
Because of unfavourable circumstances (no ship going to Holy Land) the pilgrimage to Jerusalem fell through, and Laynez with Loyola and the other Friends in the Lord (by then they were ten) offered their services to the Pope. After the Order had been definitely established (1540) Laynez, among other missions visited Germany. Laynez was a papal theologian during each of the three periods of the Council of Trent. At one point he was also professor of scholastic theology at La Sapienza.
Pope Paul III sent Laynez to Trent as his theologian. Laynez arrived at the Council on May 18, 1546, five months after it opened, with Alfonso Salmeron. Before long, Laynez was recognized as exceptional – one of the first practical consequences was that he was allowed to preach in Trent when not on Council business, whereas the general rule forbade preaching by conciliar theologians. Another exception was the three-hour time limit accorded to Laynez in the council debates, while the standard allotment was an hour.