When did Benedict XVI become the pope?

Answer 1

He was elected Pope on April 19th 2005, in a papal conclave. He then celebrated his Papal Inauguration Mass on April 24th 2005. And on May 7th 2005 he took possession of his Cathedral.

Cardinal Joseph Ratzinger was elected Pope on the 19 of April in 2005, and took the name Benedict XVI.

I take it you mean when Pope Benedict XVI was pope, or when Benedict XVI become pope. I'll answer both ways. Cardinal Joseph Alois Ratzinger a major prefect in the Roman Curia (the Holy See's government in a way) and also dean the College of Cardinals under Pope John Paul II. When John Paul died in April 2005, the College of Cardinals entered conclave on April 17 and on the two days later on April 19, the Cardinals elected Cardinal Ratzinger as pope being John Paul's successor. Cardinal Ratzinger as you know took the name of Benedict XVI. Pope Benedict led the Church from his election in 2005 to his resignation/retirement on Feb. 28, 2013 due to exhaustion and old age.

Answer 2

Benedict was elected to be the next pope by the Conclave of Cardinals on April 19, 2005 after the death of Pope John Paul II. He was officially made the Pope on 24 April 24, 2005.

Answer 3

He was elected and installed as pope in April of 2005.

Answer 4

On 19 April 2005, Cardinal Ratzinger was elected as the successor to Pope John Paul II on the second day of the papal conclave after four ballot.