Can I publish a book containing information I find on the internet about historical people or fictional characters, if I put the information in my own words?
Answer to the question:
There is no law that prevents you gathering information from the internet (or from books, magazines, journals, etc) and using that information to create your own work or works. Indeed, that's just how secondary source research works. You do however need to be aware of specific laws that affect how you go about this task. For instance: (i) copyright law prevents the copying of copyright works, and can in principle prevent the copying of some ideas (eg detailed fictional plots); (ii) trade mark law / passing off law may inhibit the use of fictional character names; (iii) access to some works may be subject to contractual restrictions. The best way to get to grips with these issues is to read a primer on publishing law. I liked Hugh Jones' / Christopher Benson's book Publishing Law (although I haven't read the latest edition).