Óscar Arnulfo Romero y Galdámez (15 August 1917 – 24 March 1980) was a prelate of the Catholic Church in El Salvador. He served as auxiliary bishop of the archdiocese of San Salvador, the titular bishop of Tambeae, as bishop of Santiago de María, and finally as the fourth archbishop of San Salvador. As archbishop, Romero spoke out against social injustice and violence amid the escalating conflict between the military government and left-wing insurgents that led to the Salvadoran Civil War. In 1980, Romero was shot by an assassin while celebrating Mass. Though no one was ever convicted for the crime, investigations by the UN-created Truth Commission for El Salvador concluded that Major Roberto D'Aubuisson, founder of the right-wing Nationalist Republican Alliance (ARENA) political party, had ordered the killing.In 1997, Pope John Paul II bestowed upon Romero the title of Servant of God, and a cause for his beatification was opened by the church. The cause stalled, but was reopened by Pope Benedict XVI in 2012. Romero was declared a martyr by Pope Francis on 3 February 2015, paving the way for his beatification on 23 May 2015. During Romero's beatification, Pope Francis declared that his "ministry was distinguished by his particular attention to the most poor and marginalized." Pope Francis canonized Romero on 14 October 2018.

Seen as a social conservative at the time of his appointment as archbishop in 1977, Romero was deeply affected by the murder of his friend and fellow priest Rutilio Grande and thereafter became an outspoken critic of the military government of El Salvador. Hailed by supporters of liberation theology, Romero, according to his biographer, "was not interested in liberation theology" but faithfully adhered to Catholic teachings on liberation and a preferential option for the poor, desiring a social revolution based on interior reform. Up to the end of his life, his spiritual life drew much from the spirituality of Opus Dei.In 2010, the United Nations General Assembly proclaimed 24 March as the "International Day for the Right to the Truth Concerning Gross Human Rights Violations and for the Dignity of Victims" in recognition of the Romero's role in defense of human rights. Romero actively denounced violations of the human rights of the most vulnerable people and defended the principles of protecting lives, promoting human dignity and opposing all forms of violence. Archbishop José Luis Escobar Alas, one of Romero's successors as Metropolitan Archbishop of the Roman Catholic Archdiocese of San Salvador, El Salvador, asked Pope Francis to proclaim Romero a Doctor of the Church, which is an acknowledgement from the church that his religious teachings were orthodox and had a significant impact on its philosophy and theology.Latin American church groups often proclaim Romero an unofficial patron saint of the Americas and El Salvador; Catholics in El Salvador often refer to him as San Romero, as well as Monseñor Romero. Outside of Catholicism, Romero is honored by other Christian denominations, including the Church of England and Anglican Communion, through the Calendar in Common Worship, as well as in at least one Lutheran liturgical calendar. Romero is also one of the ten 20th-century martyrs depicted in statues above the Great West Door of Westminster Abbey in London.