Pope Benedict XVI is proving such a bestselling author that his entire literary output before he became Pope is to be issued in thirteen volumes, with the first volume to appear in bookshops at the end of this year.

The pontiff's last book, Jesus of Nazareth — his first major publication written as Pope — has sold 2,500,000 copies so far worldwide. But there is growing demand for the works he produced as Cardinal Joseph Ratzinger, when he was the Vatican's chief expert on doctrine, and even for his writings as a German theology professor in Bavaria.

"Benedict is a cerebral theologian, but far from dry" one Vatican source said. "He writes simply and lucidly, with human insight as well as profound spirituality".

On a more worldly note, two years ago the Vatican reinforced copyright on all the Pope's speeches and writings, partly to prevent them being pirated but also because his words — like those of John Paul II, his predecessor — have a huge market value.

Father Giuseppe Costa, head of the Vatican publishing house Libreria Editrice Vaticana said that in the three years since Benedict was elected Pope, income earned from sales of his books amounted to €2 million (£1.6 million).

Father Costa said that the collected works would total 132 titles, including books, monographs and meditations, beginning in 1950 and ending with his Good Friday meditations for Easter 2005, on the eve of his election at the secret conclave which followed the death of John Paul II.

The collection will be published by the Vatican jointly with the German Catholic publishing house Helder in several languages, including German, Italian and English.

Father Costa said that many of the Pope's early works were hard to track down or even "unfindable", including his meditations on St Augustine (1954) and St Bonaventure (1959). He told La Repubblica that it had "not been easy" to persuade the Pope to sanction the venture, but success of his book sales "speaks for itself".

He said that the Pope's first encyclical, Deus Caritas Est, had sold more than 1,600,000 copies so far and his second, Spe Salvi, was not far behind at 1,400,000. However issuing the collected works was not a money-making enterprise but stemmed from a desire to promote the "great social, cultural and humanitarian value" of the Pope's thought and make it more widely available.

Father Costa said that the Pope hoped to use profits from the venture to fund a Ratzinger Foundation, with offices in Rome and Germany, which would not only act as custodian of his archive and literary output but would also provide financial support for less well off theology students.

The Pope's books as a cardinal include Introduction to Christianity; Salt of the Earth; The Ratzinger Report; Truth and Tolerance; God and the World; The Spirit of the Liturgy; Many Religions, One Covenant; Called to Communion: Understanding the Church Today; The Nature and Mission of Theology; The Meaning of Christian Brotherhood; and Milestones, a memoir of his life from his birth until 1977.

Books about the Pope are also on the bestseller lists, including Joseph and Chico: The Life of Pope Benedict XVI as Told by a Cat by Jeanne Perego, a childrens' book with a preface by Father Georg Gaenswein, the Pope's private secretary.

The Italian Catholic journal Tempi said that a new biography of the Pope, Benedict of Bavaria: An Intimate Portrait of the Pope and his Homeland by Brennan Pursell, an historian at DeSales University in Pennsylvania, would reveal that as a teenager in Hitler's Germany the Pope had a cousin who suffered from Down's Syndrome and was murdered as part of the Nazi extermination of the mentally and physically handicapped.

It said that the episode occurred in 1941, when the future Pope was 14. Professor Pursell said that it had had a profound impact on the young Joseph Ratzinger, and had reinforced his "unshakeable belief in the sanctity of life from conception until natural death".