An improvisator is someone who can create or say something immediately without prior preparation. There are many synonyms to this word, and here are a few options. A prompter, extemporizer, or ad-libber are people who can come up with something on the spot with ease. A spur-of-the-moment person or improviser is someone who can perform well without any notice. A spontaneous or impromptu individual can also be considered as an improvisator. A quick thinker or creative soul is someone who can lay down their thoughts and ideas right away. All these words define someone who can think on their feet and act without any pre-planning, making them an improvisator.