In 1760, James Macpherson, a Scots poet of the 18th century claimed to have found poetry written by Ossian. He published translations of it during the next few years. It was extremely well received at the time, however it became clear after a few years that the poems were forgeries, although forgeries of some artistic merit. The most famous of these poems was Fingal written in 1762.
The historical person was memorialized in legend under the name Oisin, a great bard and member of the Fianna.
Oisin fell in love with Niamh, the Queen of Tir na n-Og and returned with her to Tir na n-Og, but became homesick after what he though was three years. Niamh let him borrow Embarr, her horse who could run above ground, and made him promise not to touch Irish soil.
The three years he spent in Tir na n-Og turned out to be 300 Irish years and Oisin fell off Embarr, instantly becoming an old man. Meanwhile, Niamh had given birth to his daughter, Plor na mBan. Niamh returned to Ireland to search for him, but he had died.