I specifically use the word entity so as not to imply human necessarily.
By "the idea of an entity" I mean aspects such as the intellect, physical form, historical and current experiences, spirituality etc. (where such things apply).
The closest I have come is "entire being", as it is used in some literature. For example, "The dog hated the vacuum cleaner with its entire being".
I've also considered persona but I think this focuses too heavily on an intellectual aspect.
Individual seems more like a description of the disticntion between entities rather than an entity itself.
As you can probably tell, I’m having trouble even describing what I want.