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Jaap Buitendijk
Daniel Radcliffe is boy wizard Harry Potter.

In Harry Potter's world, it's only been a year since he and his friends were last at Hogwarts School of Witchcraft and Wizardry. In the real world, it's been nearly two years since we've seen their adventures on the big screen.

Production problems — some of them caused by the lengthy, often-nasty Screenwriters Guild of America strike — and other bumps in the road have delayed the release of "Harry Potter and the Half-Blood Prince," based on author J.K. Rowling's sixth novel in the series. Originally, the film was scheduled for a Thanksgiving 2008 release. But it's finally being released July 15. (Several theaters will host midnight screenings July 14.)

The delays haven't quelled Potter-mania at all, though.

In fact, online ticketing sites such as Fandango and Movietickets.com are reporting that pre-sales for the sixth film are so brisk that it may conjure up some serious box-office magic. "Half-Blood Prince" is expected to provide stiff competition for the year's biggest film so far, the second "Transformers" movie.

So before the movie is released, here's a helpful primer to bring you up to speed.

By the way, the filmmakers are already in pre-production for the adaptation of the seventh and final book, "Harry Potter and the Deathly Hallows." It will be split into two movies, the first of which is already scheduled for release Nov. 19, 2010. The second movie will be released July 15, 2011.

The main characters

Harry Potter (Daniel Radcliffe): The boy wizard with a lightning-bolt-shaped scar may be the only person who can stop the Dark Lord Voldemort, who murdered the boy's parents.

Over the course of his studies at Hogwarts, he has grown as a wizard and as a person, and he has found father figures in professor Albus Dumbledore, Sirius Black and the giant Rubeus Hagrid.

Hermione Granger (Emma Watson): Harry's female pal from a supposedly non-magical family also has come into her own. And she's come to have certain feelings for their mutual friend, Ron Weasley.

Ron Weasley (Rupert Grint): Speaking of Weasley, he's overcome his lack of confidence and has become much less bumbling than he was at first. Ron is also trying to deal with his own, conflicting feelings for Hermione.

Lord Voldemort (played by Ralph Fiennes most prominently, as well as Richard Bremmer, Christian Coulson and others): The former Tom Riddle is a dark wizard so feared that he is referred to by many as "He-Who-Must-Not-Be-Named."

While he was believed to have been vanquished, he's returned with a deadly vengeance.

Professor Albus Dumbledore (played by Richard Harris in the first two movies; Michael Gambon from then on): The eccentric Hogwarts headmaster is supposedly the only wizard Voldemort ever feared.

At times, it almost seems like he's the only person who really believes in Harry's dire visions about Voldemort's return.

The movies

"Harry Potter and the Sorcerer's Stone" (2001): Harry, Hermione and Ron all come to Hogwarts to begin their studies. They discover one of their teachers is dabbling in the dark arts and may be trying to bring Voldemort back to life.

"Harry Potter and the Chamber Of Secrets" (2002): Harry and friends return to Hogwarts for their second year, only to find danger in the off-limits Chamber of Secrets.

They also discover the diary of Tom Riddle, the Hogwarts student who became Lord Voldemort.

"Harry Potter and the Prisoner Of Azkaban" (2004): In his third year at Hogwarts, Harry gets in trouble when he uses magic outside of the school. He also believes he's in danger when the man accused of killing his parents — Sirius Black (Gary Oldman) — escapes from Azkaban prison.

"Harry Potter and the Goblet Of Fire" (2005): Harry gets to watch the Quidditch World Cup and is chosen to compete in the prestigious Tri Wizard Tournament during his fourth year at Hogwarts.

He also barely survives an attack by the reborn Lord Voldemort.

"Harry Potter and the Order Of The Phoenix" (2007): Fifth-year Hogwarts students Harry, Hermione and Ron begin building an army to combat Voldemort. However, the dark lord has allies within Hogwarts, as well as within the Ministry of Magic.