This idea was advanced by Icelandic historian and poet, Snorri Sturluson, who lived in Iceland around the 12th-13th centuries. He's most notable for writing the Heimskringla which is a history of early Norwegian Kings and the Prose Edda a pretty important book of poetry. In the Edda he posited that the Gods began as real life tribal leaders who led their peoples to victory and after their death, the funeral sites became holy sites. Then, over time as the tribes/groups called upon their dead leaders during victory or hardship, they became deified.

Prose Edda Prologue: IV The assertion for Odin as early King can be seen here

"his son was he who is named Vóden, whom we call Odin: he was a man far-famed for wisdom and every accomplishment. His wife was Frígídá, whom we call Frigg... Odin had second sight, and his wife also; and from their foreknowledge he found that his name should be exalted in the northern part of the world and glorified above the fame of all other kings. Therefore, he made ready to journey out of Turkland, and was accompanied by a great multitude of people, young folk and old, men and women; and they had with them much goods of great price. And wherever they went over the lands of the earth, many glorious things were spoken of them, so that they were held more like gods than men. They made no end to their journeying till they were come north into the land that is now called Saxland; there Odin tarried for a long space, and took the land into his own hand, far and wide."

There are legends surrounding a "real life" odin, and sometimes he is depicted (perhaps poetically) as moving north leaving the classical age.

On the actuality of this, I find it hard to believe. From what looks like the strongest claim on the internet, the argument is purely circumstantial evidence. This is as opposed to Jesus, for which we have (few, but extant) direct records of a Jesus of Nazareth who was crucified, and we have many attestations of at least a man named Jesus assuming a prophet position.

It's possible Odin could have been a real person. From what I understand, his popularity seems to have grown over the migration period, primarily supplanting Tyr. However, such extraordinary claims require extraordinary evidence, and there just isn't much of it.

EDIT: I do, however, think there is something vaguely romantic about the adoption of a sort-of "anti-roman" hero that grew popular in contrast with christianity. However, that page seems to be really grasping at straws, and provides more of an indication of a pattern (with "Further indications TBD" suggesting a polemic at the start).