Auto-complete and form auto-populate from wikipedia
To create your own autocomplete callback, you can see Textfield that uses autocomplete which shows a custom autocomplete.

Since all the data is stored of site though, you can save some time and load by implementing it client, since the user must rely on javascript anyway.

Managing JavaScript in Drupal 7 shows how to add the javascript to your site.

I'm not aware of any module, or even php/js library, that does all the wikipedia integration. If you go with the PHP option, you'll probably be interested in Guzzle. When I tried last, it was complicated to integrate composer packages with Drupal 7 though, but it looks like the situation may have improved through Composer manager.