You should look into prompt engineering, from experience it might be a bit difficult to get GPT2 to catch your prompt correctly, so if you are able I would go with a bigger model.
(Any article about prompt engineering will tell you this but, make sure you make the prompt read as something you would see in a book)
As for generating that prompt, (and this is only a suggestion) you can use a transformer to summarize the wikipedia article, and use that as the prompt. I believe HF transformers has a pipeline for that.
Cheers