Fintan mac Bóchra (Forerunner)

See also: Tuan mac Cairill, another Lebor Gabála Érenn character with the ability to shape-shift, and as a result, he lives for several thousand years.
Could be the First Ever Druid, since he can turn into animals. Perhaps the is Tuan Mac Cairill though. 
Clipped from: https://en.wikipedia.org/wiki/Fintan_mac_B%C3%B3chra
In Irish mythology Fintan mac Bóchra (modern spelling: Fionntán), known as "the Wise", was a seer who accompanied Noah's granddaughter Cessair to Ireland before the deluge. Bóchra may be his mother, or may be a poetic reference to the sea.
He was one of only three men in the expedition, along with fifty women, so he, Cessair's father Bith, and the pilot, Ladra, had sixteen wives each. Fintan's wives are named: Cessair, Lot, Luam, Mall, Mar, Froechar, Femar, Faible, Foroll, Cipir, Torrian, Tamall, Tam, Abba, Alla, Baichne, and Sille. He married Ebliu later. His only son was Illann.
His wives and children were drowned when the flood arrived but he survived in the form of a salmon, remaining a year under the waters in a cave called Fintan's Grave.[1] He then turned into an eagle and then a hawk then back to human form. He lived for 5500 years after the Deluge, becoming an advisor to the kings of Ireland. In this capacity he gave advice to the Fir Bolg king Eochaid mac Eirc when the Tuatha Dé Danann invaded, and fought in the first Battle of Magh Tuiredh.
He survived into the time of Fionn mac Cumhail, becoming the repository of all knowledge of Ireland and all history along with a magical hawk who was born at the same time as him. They meet at the end of their lives and recount their stories to each other. They decide to leave the mortal realm together sometime in the 5th century, after Ireland was converted to Christianity.
Due to his ability to shape-shift into a salmon and his honorific title as, "The Wise", Fintan mac Bóchra is sometimes confused with a similarly named animal figured in Irish mythology more commonly known and referred to as the Salmon of Wisdom.
When Fintan the Wise of the hundred lives came to Ireland before the flood he thought himself the first but found Cailleach living there, and knew her to be far more ancient than himself. 
See also
Tuan mac Cairill, another Lebor Gabála Érenn character with the ability to shape-shift, and as a result, he lives for several thousand years.
References
"Lebor Gabala Erenn pt. 2". Retrieved 22 May 2010.
Appears In
Family
Mother
* Bóchra may be his mother, or may be a poetic reference to the sea.