(Mess-gegra, Mes Gegra, Mes Gedra) was king of Leinster during the events of the Ulster Cycle, and was also the brother of Mac Da Thó aka Mes Róidia...

is actually probably Mes Róidia, the famed brugaid ('landowner', 'hospitaller') of Leinster and the brother of King Mes Gegra, as attested by a genealogical...