Dear Reader,
I know that the headline of this post sounds like a combat scene involving Pokemon or something similar. (By the way, if there were Pokemon with those names, I might actually play the games.) These are actually two different spiritual constructs. They can in many cases be used interchangeably but if you are going to be technical about it, they have different uses and are formed differently.
Let's start with the Egregore. You may have read about some chaos magicians creating Egregores or possibly read some really
old stories about Egregores having gone astray and causing havoc. There's a particularly racist and horrible one out there about Golems, which is completely wrong about what a Golem's function is and the story paints Jewish people as horrible monsters. That story dates back to the Medieval period of European history but there are assholes who like to bring it up and use it to scare people. If you want to know about Jewish ritual magic, ask a Jewish person who is into the occult. You may get lucky and they'll actually answer a few questions. Likely, they're not going to because Jewish occult magic is a fairly closed tradition for lots of good reasons.
An Egregore is a relatively modern invention. The first recorded description of a ritual to produce an Egregore can be found in the writings of the Theosophical society and of the infamous Alistair Crowley. Some can argue that the modern ritual foundations have roots that go farther back to the writings of John Dee (the somewhat infamous adviser and court astrologer of Queen Elizabeth I). Ceremonial magic records being something of a shit-show between people trying to keep their language coded to keep 'trade secrets' and avoid the ire of witch finders, it's hard to really pin down the origins of the use of Egregores. There are documents that we still haven't been able to translate that date into the Medieval period (I'm looking at you, Voynich manuscript.) that I'm certain describe ceremonial magic as well as alchemical materials.
Egregores as they are used today are entirely different from spiritual constructs from antiquity which is why I say that they are a modern invention. In the case of an Egregore for the modern chaote, it is a construct built upon a set of rules and infused with spiritual energy and the focused mental effort of a group of people. An Egregore being developed is not that different from standard spell craft, except for the focus is on the development of a spiritual entity that is to serve a specific task and last for a predetermined period of time (in the most general sense, there are obviously differences in this from spirit worker to spirit worker).
A Servitor is a similar construct built upon a set of predetermined rules. The Servitor is created by a single individual and works for them for a specific task and for a specific time period. (The term Servitor comes from the word servant.) Servitors have been around for a long time. It is possible that the spirit familiars of witches in antiquity were Servitors. It is difficult to tell because the difference between a Servitor and a spirit familiar is subtle and most won't note it upon initial inspection. A Servitor is fueled by the repetition of focus by the caster, where as the spirit familiar has its own source of spiritual energy - themselves. Servitors operate for a single practitioner and will resist if not out right reject commands from other practitioners. Egregores are similar in this fashion but they have the capacity to interact with a wider range of individuals after a certain point of collective focus and empowerment.
Poorly constructed Servitors or Egregores can have harmful results for the practitioners and people in the immediate vicinity. Stories of seances turning chaotic are more typically cases of an Egregore getting accidentally created with out rules and limitations, thus raw psychic energy is running amuck. (Now this is where if you are working with a skilled psychic who can direct the raw psychic energy of the participants, you can tone down the chaos and actually summon the one you're looking for. It requires the ability to channel and direct the psychic energy into the summoning. But that's a topic for another day.)
Egregores can be tricky to deal with when they get out of hand. There's an old expression, don't summon something you can't lay to rest. It's especially important in handling spiritual constructs. Trapping them in a container of some sort is a traditional method of dealing with them. Banishing them is also an option but you must be prepared for them to pop back up again if the circumstances resemble either those of their generation or the summoning process. Egregores have limited intelligence. Thus they will not entirely recognize that they're not being summoned when someone who is part of the group is doing something similar to the summoning.
There are also Egregores that are part of pop culture and internet culture. They're a bit more powerful than one that is produced by a small coven. They have more intelligence because there is more psychic energy behind them and more intent poured into their existence. Thus, it may happen that someone who is attempting to work with Loki, for example, get the Egregore!Loki and things get weird. Less popular deities have fewer Egregore impersonators out there. Telling the difference between the Egregore and the actual deity you're attempting to contact is difficult. Consulting a priest of that deity or a spirit worker who is intimately familiar with the deity is advisable in these situations. A lot of the 'bad behavior' attributed to deities is actually a result of an Egregore left to run its programming in the wrong environment. In some cases, it is because of the programming of the Egregore to begin with.