Áed Ua Crimthainn

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

[4] Áed was a friend of Finn mac Gussáin Ua Gormáin, bishop of Kildare and abbot of Newry, who sometimes collaborated with him.

In the Book of Leinster, he was apparently the first scholar to create the concept of the rí Érenn co fressabra, the "king of Ireland with opposition", later more widely adopted.

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.

[7] This has been called the oldest surviving personal letter to have been written in Ireland,[12] although this ignores earlier correspondence between Irish bishops and the archbishops of Canterbury.

[1] However, at the end of the Book of Leinster, the writer added this reservation: But I, who have written this history, or rather fable, give no credence to the various incidents related in it.