Fionn The Warrior

Fionn MacCumhaill is the name of a mythical Celtic warrior, who was the leader of a band of warriors named Na Fianna at around the time of High King Conor McArt.
There are various tales about him, as part of the fiannaíocht, the name of the oral tradionition covering

his childhood, raised by warrior women
his acquiring of the wisdom of "The Salmon of Knowledge" ,
The death of his father,
His joining of Na Fianna, assuming leadership of Na Fianna ( his father role),
How he got his name "Fionn" and how his hair turned white,
The birth of his son Osin,Oisin visit to "Tir na No'g,
Other loves of his life,
The Giant's Causeway and his battle with a Scottish giant
Fionn's chase of "Diarmad agus Grainne"
and ultimately the story of his death.

And there's plenty plenty more, to confuse matters there are different versions of the tales, and there are different chronicles too in the mythology of other Celtic nations.

There is artwork, famously by Jim Fitzpatrick who has made faboul stain glass windows depicting variosu Irish legends.

Also there is another (skywalker). there is CuCullain , who belongs ot teh Ulster cycle or the .

He also has his own Wikipedia page; Wikipedia is known for being very accurate with sciencey stuff and open to abuse in relation to entries on people, As Fionn is a person albeit possibly completely imaginary, I cannot possibly vouch for the authenticity of detaisl on this page, but many of them are true. :-) However, as I have said before as there are more than one version of some of the tales, then of course there is more than one version of the truth.
these various truths cannot be compared to the way in which there is a difference between Large Scale (classical Newtonian Physics) and Quantum Mechanics (or at least at the time of writing there is a big difference, as far as I know there is not an accepted Grand Unifying Theory or Theory of Everything... again you can look these up on Wikipedia).

Glossary
In Irish the definite article "the" can be singular "an" or plural "na".
agus =and
Tir na nOg means land of youth, Og is the word for youth, but the "n" is added ,
this "n" is an uru or eclipse and is a typical construct used in certain tenses and cases ( such as the genitive case ) in the Irish language.

At the time of writing there are plenty of Irish resources on the web (ADD LINK to SEARCH page), here are a few which I have "google'd".

[TODO Include DICTIONARIES I use in that LINK]