Born in Düsseldorf in 1932, Dominican Ambrosius Eszer worked as a professor of Partristics and Eastern Church History at the Pontifical University of St. Thomas Aquinas ("Angelicum") since the 1970s. From 1983 he worked for the Congregation for the Causes of Saints of the Roman Curia and from 1990 until the end of 2008 was its General Relator.

Eszer grew up in Düsseldorf and, because of his father's profession, in Großgießmannsdorf near Neisse in Upper Silesia. After surviving the difficult war years, he graduated from the Fischer-Gymnasium in Euskirchen. He was strongly committed to the new "CDU" party. At the beginning of June 1952, he entered the novitiate of the Dominican Province Teutonia in Warburg, studied at the religious college in Walberberg near Brühl and was ordained priest in 1959.

He had been a member of the Dominican Historical Institute at Santa Sabina on the Aventine in Rome since 1954 and was awarded a doctorate (Dr. scient. eccl. orient.) at the Jesuit-run Institutum Orientale. He also attended the Vatican School of Diplomatics and Palaeography. From the 1970s onwards he worked in Rome as Professor of Partristics and Eastern Church History at the Pontifical University of St. Thomas Aquinas ("Angelicum"). From 1972 to 1975 he carefully directed the Roman Institute of the Görres Society, as can be seen from his precise documentation in the archives.

Eszer had worked for the Congregation for the Causes of Saints of the Roman Curia since 1983 and was its General Relator from 1990 to the end of 2008. The task of the General Relator is to prepare the beatification and canonisation processes and to evaluate the necessary files. Eszer was in charge of the trials of Clemens August Graf von Galen, Sr Maria Restituta, Ladislaus Batthyány-Strattmann, Emperor Karl I, Titus Horten O.P. and Franz Jägerstätter, among others. Edith Stein (Sr. Benedicta a Cruce) was especially close to his heart. Eszer was a real "Teuton" in Rome, straightforward and cordial, sometimes grumbling, enormously hard-working and unpretentious, and completely unpretentious.