1. Ailill mac Mágach of Connacht The most famous Ailill--king of Connacht in the time of the Ulster Cycle, Ailill is the husband of Medb, and son of Ross Ruadh of Leinster and Mata Muresc of Connacht. As his older brothers had won their own kingdoms, Ailill was left Connacht through his mother Mata. He married Medb, daughter of the ard righ. It was to Ailill and Medb that Oengus mac ind-Og came when he was in pursuit of Caer the swan woman, and it was to Ailill and Medb that Fergus mac Roich came when he was exiled from Ulster by the usurping Conchobor mac Nessa.
Medb sought parity with Ailill, especially as she was daughter of the ard righ and constantly sought after by many men, while Ailill had won his kingdom by default. And so, Medb tallies up their possessions and found them equal, except that Ailill owned a white bull named Finnbennach. Medb, seeking to make herself completely equal with Ailill, then attempted to gain the Donn Cuailnge (brown bull of Cooley) from Conchobor of Ulster. When he refused, this leads to the Tain Bo Cuailnge.
His daughter Finndabhar is sought by the hero Fróech mac Fidach, who refuses to pay the high dowry for the princess. Ailill fears that Froech will simply abduct her (having already played mischief at the court), and so Ailill attempts to have a sea monster devour Froech as he swims. Instead, Finndabhar dives in with a sword to help him. As this happens, Ailill finds Finndabhar's lost ring in Froech's clothes on the lakebed. He throws the ring into the water, thinking that Finndabhar had betrayed her father and given it to Froech. Later, after several attempts to kill Froech fail, Ailill demands the ring from Finndabhar, or he will kill her. Instead, the giant salmon who attempted to kill Froech is brought forward in a feast, and the ring is found, saving Finndabhar and Froech. (The Ring in the Fish is a common motife in Celtic and other mythologies.) Ailill is chagrined, and must allow them to then marry.
Both Ailill and Medb were sexually promiscuous, though Medb was more jealous than Ailill. This jealousy lead to Medb tricking her lover Conall Cernach into killing Ailill as he met with another woman. Ailill placed a curse on Conall Cernach, however, causing Conall to break his geis, and causing his own death in return.
2. Ailill Anglonnach (One Stain) or Aillil Anguba The brother of Eochaid Airem. He fell into a wasting sickness for Étaín, the wife of Eochaid Airem, who was, in fact, a reincarnated goddess who had been married to the god Midir, only had lost her memory in this reincarnation. During this sickness, he confesses to Etain that he loves her, and she agrees to meet with him in a tryst. Unfortunately, he falls into a deep sleep and misses the tryst. Instead, Midir appears in the shape of Ailill to take Étaín back to the Tuatha Dé Danann. Midir reveals that he had put Ailill under a spell to fall in love with Étaín for this purpose, and then releaves Ailill of his wasting sickness.
3. Ailill of Ulster: the father of Étaín.
4. Ailill Agach (Edge of Battle): father of the hero Maelduin. While on a rampage, he raped a nun, who became pregnant with Maelduin. Ailill is then killed by some Leinstermen, and Maelduin must struggle with himself whether to avenge his father's death. Oh, very Hamlet indeed, with ocean voyages and everything. ("The Voyage of Maelduin")
5. Ailill Aolum: a legendary ancestor of the kings of Munster, supposed to have died around 227 CE. One stories says he raped the goddess Aine, who then slew him with her magic.
6. Ailill Áine: son of ard rí Loegaire Lorc (ca. 300 BCE), he was slain by his jealous uncle Cobthach the Meager, who wanted the throne of Ireland. However, Cobthach missed Ailill's son Moen Ollam, who avenged his death and regained the throne. ("The Destruction of Dind Rig")