"Vikings" is a Historical Fiction Drama about the life of Ragnar Loðbrok - a character who was potentially, even possibly, real, but primarily existed in Viking myth.
I say "fictional" and "drama" for that is what it is - there's no two ways about it that this is certainly not what happened in myth, or in history, but that doesn't stop this series from being one of the most moving, most emotional, and somehow, most relatable shows of all time, despite following Northmen from the 9th century.
I've watched up to the end of Season 4, and slightly into Season 5, and I intend to keep watching, even though I have heard less favourable things about the last two seasons.
An amazing story about a man who did not seek power, but was forced to take it, by, as Ragnar himself says "Other people's actions".
If you have Netflix and are thinking of watching this show, then I would definitely recommend it. The only other thing I can advise is that this show does live up to it's MA15+ rating, so I would not advice it for younger viewers.
I was planning to write a really long review on the characters and their motivations and writings, but I ran out of space :_(