King (a ruler)
The position of the ruler (king, jarl, konung, knjaz, vladyka etc.) was very different. It depends of time and concrete tribe(s). There were even societies where there was no ruler (like for example the confederation of slavic Lutici tribes). In the contrast there were also very powerful kings, who ruled vast lands (e.g. russian Kjaz). So I will focus here only on those smaller, local chieftains - as in pagan reality it was more natural to have such rulers than some great kings.
Depends on times, once ruler was more powerful and once common gathering was the mightest power center. The only thing is known for sure - there was never pure democracy in such societies. The thing was a tool in the hands of an elite (including chieftain). The free people could only accept or reject proposals of nobles. Of course people could influence noblemen to take care of some things, but still the noble ones were those who presented the case on the thing.
In ancient times the king was someone who represented tribe in the outside. That means that he had to be as perfect as possible - because in some way if the king had flaws also society had them. The most rigorous were celtic people. In those societies if the king was hurted in the battle he automatically looses his title. It was a kind of magic, as king was also becoming an half-god after his death. He was worshipped as a hero - a personification of tribe's might.
OK, but let's say that you live in a pagan society and you desire to be a king? First of all, you have to be chosen by a thing or in a divination. The latter way is more charachteristic for celtic tribes, were the layer of druids had been very influencial in politics. But both methods had a common goal - to choose somebody who is a give warrior. The main function of rulers was to lead an army to the battles. The rest of the power was supposed to be in the hands of the thing. And that's why the personal skills of the king were important. If he wanted to be powerful - he had to gain a favor of his army. Because army was constructed from free people - the same free people who were voting on common and local gatherings.
OK, you're a king now. You have won many battles, and you have a big authority amongs people. What's our next step? Of course you want to convince people that your son should take a reign after you. Because after a death of one king the new one was always chosen by a thing. But if you change it, your dynasty can gradually gain more and more power. Eventually a thing could become only an representative gathering - without any real power. It was not easy though, because the dynasty had to be not only skilled warriors, but also they were supposed to be in good relationships with the noblemen. It was difficult especially when those both social layers were divided by fighting for their own buisness and rights.
Nobility and free people
To see what a difference was between ordinary free people and the nobility we need to study the roots of those division. At the beginning the elite was built up from people who were brave enough. The people who were a good leaders or tradesmen eventually got big assets, and what's important a land. Many between peasents ("ordinary" free people) also had a land, or even servants - yet their property or status hadn't been big enough to count in the society. So as we can see those two layers were very unstable - if you was good enough and had some luck, you could become one of those mighties ones. It may be strange for people who associate only knights with the military, but we must remember that in fact every free man was supposed to fight in defence of his land. Moreover - because noblemen were expected to give much harder effort during a war sometimes it was more profitable to be an "ordinary" freeman! (e.g. in the times of Charlemagne, in purely frankish areas, when the nobility had to serve in wars for many years unlike the rest of the society).
About mentioned luck - pagan people (and people in general, even very long time after a "baptism" of a tribe) believed that if you are wealthy and you are good in the battle - than the gods are on your side. That's why very often "lower" situated people were agreeing with ideas presented on the things with no objection - because they believed that talented elite, who are supported by gods will make best decision for the whole society.
Nobility, beside their obedience in society, had also another privileges bounded with a law. E.g. they were taking bigger compensation for killed relatives, grievances etc. Usually they were taking two or three times more "money" (or wealther) than a usual person. Later it changed - the christian kings, who wanted to protect their officials or gain a hearing from the nobility where raising these amounts. Also during a trial their vote was two or three times more important than a voice of "regular" men.
With noble blood were bounded also noble duties. The most important was to defend a tribe, but not only. Keeping a peace in society and such things were also important. If a noble men failed, than he was the only person who got punished. Also if he broke a law, he was paying more - because he was expected to be more ideal than other free people. The nobility was expected to be an example and inspiracy for the other tribesmen - and not a tool of tyranny in the hand of the king, like it became often in the christian times.
Here I make it short - a slaves weren't treated like a human beings according to law. If you read any agreement between two persons about inventory etc. you will see that very often a slave costed less than a cow - because cow is more useful. Even if icelandic family sagas present us that enslaved people weren't very often treated badly, in fact they had no rights. When you become a slave you loose everything - including your kin. And a man without a kin was nobody - because no one would take his side in a trial, no one would give you a shelter etc. Doing this was highly comdemned by ancient societies. The master of such slave could kill him, rape him/her or make him hurt without any consequences. The only situation when somebody was supposed to pay for a slave's death was when he killed someone's enslaved person. It was treated similar to killing a horse or a cow.
In the eyes of people from that times when somebody gave a slave personal freedom - than in some way he was creating him a human again, and becoming some kind of father for him.
In germanic societies there was also a layer of lits, but I will write about it after an article devoted to women. Also there will be article about the priests - as they were something more special than other free people.
Karol Modzelewski - Barbaric Europe ("Barbarzyńska Europa")
Icelandic family sagas, (like Laxdoeala) codex of germano-roman rulers (like longobard Liutprand, Charlemagne and others)
Unfortunetely other books you have to find for yourself - as most of the literature about this subject I've learnt from mentioned book and some articles on the internet written only in polish. Yet those two sites should be helpful:Icelandic Saga Database
Written by Vladyka in the year 2013.