Áed was a scholar and a descendant of an old ecclesiastical family of
County Laois who were the
comarbai (heirs) of Colum moccu Loigse, the 6th century founder of the religious house of Terryglass and a friend of
Colum Cille. Both Finn and Gilla na Náem Úa Duinn assisted Áed with compiling the Book of Leinster. According to a note in the Book of Leinster, "Áed Ua Crimthainn wrote the book and collected it from many books". It is a literary compendium of stories, poetry, and history, and it appears from
annals included in it that it was written between 1151 and 1201, although largely completed by the 1160s. Áed was probably the court historian of
Diarmait Mac Murchada. In the Book of Leinster, he was apparently the first scholar to create the concept of the , the "king of Ireland with opposition", later more widely adopted. This described Diarmait's ambitions and the achievements of his great-grandfather
Diarmait mac Maíl na mBó. Áed's description of the period between the death of
Máel Sechnaill mac Domnaill and the rise of Diarmait mac Maíl na mBó was misread by Conall Macgeoghegan when he compiled the so-called
Annals of Clonmacnoise in the 17th century, leading to the inclusion of poet Cuán Ua Lothcháin and abbot Corcrán Clérech in some old lists of
High Kings of Ireland. A letter from Bishop Finn to Áed was copied into the Book of Leinster, at folio 206, by one of the other hands of the manuscript. although this ignores earlier correspondence between Irish bishops and the archbishops of Canterbury. The letter reads: Áed respected Irish tradition, even when it offended his religious beliefs or his educated sense of reason. However, at the end of the Book of Leinster, the writer added this reservation: ==Notes==