The Irish god credited with inventing the Ogham alphabet is Ogma.
Ogma is a member of the Tuatha Dé Danann, the supernatural people who feature prominently in Irish mythology. He is associated with speech, eloquence, poetry, learning, and martial strength. In the medieval Ogam Tract, Ogma is described as the inventor of Ogham, creating it as a learned form of communication.
Historically, Ogham was an early medieval writing system used mainly for Primitive Irish and later Old Irish. Its letters were formed from groups of lines and notches cut along the edge or face of stone, wood, or another surface. Roughly 400 early surviving stone inscriptions are known, many in Ireland and western Britain.
The mythological attribution and the historical origin are not identical claims. Medieval tradition credits Ogma, while scholars debate how the script developed; Latin influence is often considered important. Ogham is sometimes called the “Celtic tree alphabet,” but that description mainly reflects later interpretations of letter names and is not a complete account of its original use.