Áed Ua Crimthainn

Áed Ua Crimthainn (fl. 12th century), also called Áed mac Crimthainn, was abbot and coarb of Terryglass , near Lough Derg in County Tipperary, Ireland. 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:

Life and health from Finn, bishop (i.e. of Kildare) to Áed mac Crimthainn, lector of the high king of Leth Moga, and coarb of Colum son of Crimthainn, and prime historian of Leister in wisdom and knowledge and book lore, and science and learning. And let the conclusion of this little tale be written for me. You may be certain, o keen Áed, o man of great beauty, whether I be a long or a short time without you I would like you to be with me. Let the poem book of Mac Lonáin be brought to me so that we may study the meanings of the poems that are in it, et vale in Christo. However, at the end of the Book of Leinster, the writer added this reservation: