I'm not of course going to just give the answer in the first sentence, instead, I am going to walk through a few options and then let you think before I drop it on you.

Is money the ultimate power?

It is pretty high up there, because it is readily traded for all kinds of capital. Capital is nothing to do with the Head or the Top. It is from the latin root word 'to grasp': 'capit'. Yes, the same root as capture, captivate, and now you know it is the root of the word 'capital' which means, that which you have taken control of.

In modern alphabetic languages, capital letters are big, yes, but their meaning is to indicate the word is a noun. The germans especially are obsessive about them, and I think they invented the idea. If you know german or are familiar with german text, then you would recognise that the taller letters are used for names of things. In other languages that developed earlier, the word The, the definite article, was often used this way, you can see this in especially slavic languages where in the same way as the Nordic peoples use suffixes, often a word has this suffix attached in exactly the same context as a german noun.

Is influence the ultimate power?

Influence is where one person's ideas infect other people and cause them to work to support the idea. There is two sources of influence, that being admiration and fear. With only the use of violence, you can influence people, but it has a very high cost in blowback. Eventually the people will turn on you.

Admiration can give power through people wishing to emulate you, but like fame itself, the source of influence, it is fickle and one day someone else might say just a couple of words and suddenly you are hanging from a rope.

Is violence the ultimate power?

As mentioned in the previous, violence can create influence. But it is a very expensive type of influence that damages everything around it, including the economy, and this and many other factors causes violence to be an inferior type of power.

So what is it then, O Sage Loki of the Endless Wall of Text?

Well, I'm glad you asked, I have no idea what prompted you to ask such a question!

Control of information is the root of all power

Reputation is from information. Money is a type of information. Violence is a type of information. Humans act on information, as the central praxis of human action is to seek to use information in order to relieve discomforts. By discomforts, I don't just mean a toothache, I mean even such things as having to walk out the back to the well every day to bring water to cook, or chop up wood to light the fire in the hearth to warm the house or cook food.

The greatest enemy of entrenched power is the information regarding the violence that backs it. You cannot hold a territory without various kinds of force impeding access to other people. You cannot take a territory without this force, but you can't just throw rocks at it, usually they already thought of that.

In warfare, the most important thing is knowing the size, location, armaments and manpower of the enemy that you wish to vanquish. A war can be started, or ended, by just a few words that reveal information or distort information. A usual sign of the coming of war is the stopping of information from an enemy, as the number one way in which you prevail in war, is by knowing your enemy, and yourself, and planning action that uses this information in order to most efficiently undermine theirs.

As Sun Tzu says, the greatest victory is that where mere words topple your opponent. In some martial arts, even, there is techniques you can learn where you need only make a gesture that triggers a reflex in the enemy and then they are under your control, on the back foot.