Making a Great Old One patron is the most confusing patron to work with for most D&D groups. Devils are very straightforward. You have a contract, folklore, etc. Other patrons are more understandable, but for us, a Great Old One is meant to be something beyond our understanding.
Making a great old one patron is different than normal patrons. Their reasoning and pact do not need to make sense or be malicious.
This is something that many people don’t understand with great old ones, so let’s dive into how to create an amazing Great Old One patron!
Making the pact

Instead of making a Great Old One patron first, let’s look at the pact.
A Great Old One does not need to have a clear reason to make a pact like a devil would. Devils need souls, and other creatures want something out of the people who make deals with them. Great Old Ones don’t usually need things, but they could desire something.
The most common thing that a Great Old One wants is freedom.
Freedom doesn’t have to be immediate. Most players and DMs try to instantly free the Great Old One with the player’s help. They could get a specific item or 5 to help unlock the prison of this being, but Great Old Ones do not need to work like this.
Great Old Ones have been imprisoned for time immortal. It could be before the universe even began, but they have been there for a long time. Why not wait a little bit longer? What if the seal isn’t something that makes sense?
Most old ones do not need to be free right away. Other Great Old Ones will want to influence reality with whatever their reasoning is.
For example, there is a character in my campaign who has been influenced by a warlock. This little orphan made a pact with a Great Old One and now has OCD when there are 2 or 3 of anything. It can be people, chairs, houses, etc but if there are clearly 2 or 3 she has to count them.
Why? Who knows! It could be to free the Great Old One, or it can be just to count those numbers more often.
Pacts do not have to be harmful to the user, but they will most likely have an influence on how the user acts.
There is an infinite number of reasons why your patron can make a pact with your player, and it does not have to make logical sense. That is the beauty of the Great Old One pact.
In addition to this, Great Old Ones do not need to make a pact the traditional way. A player could be calling out to ask for help in a time of need and an ancient power hears them. They grant the player powers in order to help the Great Old One in whatever manner they need.
If you want to learn more about making the pact and what it could be like/how it affects the warlock, check out our article on how to roleplay a warlock.
After you have figured out the reason, logical or not, you are able to make your great old one.
Making a Great Old One patron
Making a Great Old One patron is going to take a lot from why the pact was made. If a Great Old One just wants to be free, then that tells you a lot about them already. This being has been imprisoned, by something, and has a way to become free.
If your Great Old One wants the player to count numbers as part of the pact, that means they are beyond our comprehension. You can make a few basic concepts like its name, origin (possibly) and history. Beyond that, it is an eldritch horror from Lovecraft.
As you can see, making a Great Old One patron can range from logical to illogical. This makes a great old one able to be literally anything the DM desires and it works! Even if something doesn’t make sense, that is the point. Great Old Ones are different than other gods though, and that is something that needs to be discussed.
Great Old Ones are beings of immense power, possibly even more powerful than the gods.
They almost always exist before time itself, or before the creation of every other being. The Great Old Ones are even rumored to be the progenitors of Mind Flayers and Aboleths.
The fact that Great Old Ones are not openly known, but have an effect on current existence needs to be ironed out before a session. How do they have an impact on people even if they are imprisoned, or dead?
Great Old Ones might not be able to die. It is possible that they are more of a concept of reality given form. This could mean that these Great Old Ones are the essence of anger, fear, or some other primal instinct.
Being the essence of something is much different than having it as your domain. If your domain is dreams, then you have control over dreams. If you are the essence of dreams, dreams are a part of you and to kill you might mean the death of all dreams. This is impossible, so your death is impossible.
Aside from the desire or lack of desire that a Great Old One has, you need to figure out what they are before you incorporate them into your game. Nail down exactly what these, or at least this being, is.
This is a confusing state, so we need to talk about if Great Old Ones are evil or just bad for their followers.
Are Great Old Ones evil?

Some Great Old Ones are evil, and some are not. Making a Great Old One patron does not mean that they are trying to harm their pact maker. These Great Old Ones might actually try to help the pact maker, but do a poor job at it. In order to grant power, they also grant insanity to the individual in some form.
Great Old Ones are not making pacts for souls or trying to screw over your players. They just want something and your players are willing to make a trade. Power for helping the Great Old One.
Now, your Great Old One might actually want to do something terrible to the world. These creatures are more ancient than the gods. Anything that they want is most likely an affront to the current state of life and to help them will cause the ruin of everything. That is worst-case scenario.
If your Great Old One has a motivation to do something like this, then they are not going to be evil towards the player. The player isn’t the thing that is being targeted like a devil would target their soul. Instead, the Great Old One just wants to target reality. If the player is a bistandard of that then it is just a small casualty. Nothing personal.
In this instance, most Great Old Ones are not evil. Just neutral and most likely chaotic. These Great Old Ones might just want reality to return to how it was. Before everything became sorted out. I honestly don’t know if this is evil, but that is up to each DM.
For Great Old Ones that have malicious intent towards everyone, such as being angered that they were overthrown by these creatures, it makes their motivations eviler. They are more willing to harm other creatures and possibly kill them instead of change their being to a subjectively better state.
Conclusion
Making a Great Old One patron is different than your normal warlock patrons.
Great Old Ones do not have to worry about reason, logic, or work in the same way that other patrons do.
Great Old Ones have their own reasons for helping the warlock and can make a pact in untraditional ways. A call for help might be enough to give the Great Old One a contract.
This contract reflects what is important to your Great Old One and tells a lot about who/what your Great Old One is. Use the contract to help you backtrack and understand what monstrosity you have created.
Just remember that Great Old Ones are not like gods. They are different and much older. It is up to the DM to figure out how they are different, but there should be a good reason why these beings are able to influence reality even though they are removed from it.
I hope that this has helped you in making a Great Old One patron. Now go forth and make your eldritch (maybe even Lovecraftian but not necessarily) horror!
This has been Wizo and keep rolling!