A Tulpa as they are called in Tibetan Buddhism are an extremely fascinating subject to study as well as to experiment with. Many of us are familiar with this concept if you had a creative childhood with the creation of imaginary friends. In the western world giving life to an imaginary friend or creating an entity are called thought forms.
You can give a thought form any character traits that you wish as well as giving a specific lifespan. One of my favorite books on this subject is called, Creating Magickal Entities: A Complete Guide to Entity Creation.