Copyright and trademarks are confusing animals.
There are 3 ways of protecting work, marks and ideas. These are Copyright, Trademark and Patents.
Copyright relates to an actual created work (think of the actual 7 books of Harry Potter). Also photographs and works of art, as well as films and TV programs for example can't be reproduced without authorisation from the copyright holder. Copyright does not need to be registered - copyright is automatically created when any new work of writing, artistry, photography etc is created.
You're possibly right about the copyright expiring 50 years after death in some countries, Snow. In general here in the UK, copyright remains for 70 years after the author's death, but there are different rules for different circumstances and in different parts of the world. More good details on UK copyright are at
http://www.copyright.gov/circs/circ1.html
Trademark relates to a mark or name. In the UK (and possibly other countries), as far as I understand, trademark often (maybe always?- I'm not certain) relates to a type (or types) of thing. Think of Mars relating to foods, for example. A company using the name Mars to sell crisps would be in breach of whoever owns the Mars Bars foods trademark. However, Someone using the name Mars to sell digital cameras (buy Mars digital cameras for an out of this world pixel resolution) would unlikely be in breach because digital cameras are not a food. Whether anyone owns the Mars trademark for such types of electronic or photographical goods would need to be investigated though.
The name Harry Potter relating to a book character (and other names used by JKR too) would therefore be protected by trademark. This is actually part of how Broomsticks and Owls got its name.... I didn't want to call it Harrypottersomething, otherwise the site would have always been at risk of being closed down for breaching the HP trademark. Actually, thinking out loud, I wonder if that's why another quite popular forum which actually did have the HP name in its site name has recently closed down.
Trademark doesn't always need to be registered - first use of the Mark is importantly considered. Registration is helpful and probably advisable though.
The third type of protection,
Patents, applies to ideas, designs and formulas etc, for example the formulas for new pharmaceuticals, or an idea to make a new type of hexagonal computer which hovers on a cushion of air and uses ants in its central processing unit. I'm not absolutely certain but I think Patents need to be registered.