The Four Cycles

A Reader’s Guide to the Mythology Behind the Trilogy

3 May 2026 ~ 3 min read

I teach World Music at the college level, and one of the things I’ve learned is that people are far more willing to explore unfamiliar traditions when someone gives them a map first. Irish mythology has one of the richest literary traditions in Europe, but it can feel impenetrable if you don’t know where to start. So here’s your map.

Irish mythology is organized into four great cycles, each with its own era, heroes, and concerns. The Mythological Cycle is the oldest and the grandest—the stories of the Tuatha Dé Danann, the gods and supernatural beings who ruled Ireland before humans arrived. This is where you’ll find the Dagda with his bottomless cauldron, Brigid the goddess of poetry and healing, Lugh of the Long Arm, and the Morrígan—the shape-shifting goddess of war, fate, and sovereignty who became the heart of Book 2 of the Cosmic Janitor Trilogy. These aren’t distant, abstract deities. They’re local, specific, and stubbornly Irish.

The Ulster Cycle is the warrior tradition—the stories of Cú Chulainn, Ireland’s Achilles, who defends Ulster single-handedly in the great Táin Bó Cúailnge, the Cattle Raid of Cooley. If the Mythological Cycle is about gods walking the land, the Ulster Cycle is about humans trying to live up to what the gods left behind. The emotions are enormous—love, honor, betrayal, and a kind of doomed heroism that makes Greek tragedy look restrained.

The Fenian Cycle shifts the tone entirely. These are the stories of Fionn mac Cumhaill and the Fianna—wandering bands of warriors who live outside settled society, hunting, fighting, and composing poetry in the forests. Where the Ulster Cycle is epic and tragic, the Fenian Cycle is romantic and adventurous. Fionn gains wisdom by tasting the Salmon of Knowledge. His son Oisín travels to Tír na nÓg, the land of eternal youth, and returns to find centuries have passed. These stories feel like the ancestors of every fantasy quest narrative ever written—because they are.

The Historical Cycle, sometimes called the Cycles of the Kings, blends mythology with actual Irish history—legendary kings, dynastic struggles, and the slow transition from pagan to Christian Ireland. It’s the most grounded of the four, and the one that reminds you these stories weren’t entertainment. They were a people’s way of explaining themselves to themselves.

All four cycles run through the Cosmic Janitor Trilogy in one form or another. The Morrígan comes from the Mythological Cycle. The sense of doomed loyalty that drives Seán echoes the Ulster tradition. The wandering, the questing, the poetry—that’s pure Fenian. And the insistence that gods and humans share the same Irish soil? That’s the thread that ties all four cycles together, in the old stories and in mine.

~ Liam