Who: By many accounts, the Dagda (or Daghda) is the Celtic god of the Earth. Known as the Good God, the Dagda is quite often called the King of the Danann, and is the son of Dana (Danu) and Bile (Belanus) and the father of Brigid (Brighid) and Aengus mac Og. The Dagda is also a partner of the Morrigan.

What: The possessor of a vast cauldron from Murias, it is said that "no company ever went from it unthankful". He was also in possession of a club or staff, that could either give or take life.

When: The Dagda is associated with Ostara, celebrated around the Vernal or Spring Equinox around March 21 or 25. Ostara is a time to celebrate the arrival of Spring, the renewal and rebirth of Nature herself, and the coming lushness of Summer. It is at this time when light and darkness are in balance, yet the light is growing stronger by the day. The forces of masculine and feminine energy, yin and yang, are also in balance at this time. (More about Ostara).

I am just going to add a few more facts here that are generally deemed important. Debi

The Dagda has also been called the Irish ‘Lord of knowledge' and Aed, meaning "Fire". He was a sorcerer, ruler over life and death, god of the earth's fertility, as well as being a near superhuman warrior. The Dagda could change the seasons and control the earth's abundance. He was originally the supreme leader of the Tuatha de Danaan and, as Ollathair ( athair translates to, 'father') (Ollathair meaning 'All-Father'), he ruled the world.

After the Milesians defeated the Tuatha, the old gods went underground and the Dagda divided up the lands and gave these 'fairy mounds' out to the Tuatha de Danaan.