I can give this stuff out seen as it pretty much has no effect on the Animation's Story and is only used as backing for his character. So its not technically spoilers.
Gindew is a Human who has the strange ability no not age, His age is unknown but he has stated "I like to think myself as 3000yrs old seen as i don't count". Around 1000yrs before the story begins, he arises victorious over his rival The Greater Knight and ends The War for the Overworld, a dreadful conflict which left the Overworld scarred.
However when the story picks up, Gindew has taken the route of a simple living, he vary rarely leaves his Home in Arraman. However he is occasionally called ever few decades to fight for the many King's of the Empire and has a strong friendship with the Empire and it's allies.