One of the biggest debates within the Potterverse is whether or not Michael Gambon was the perfect Albus Dumbledore.

There are several fans who thought he wasn't very convincing as the replacement for the late Richard Harris in the "Harry Potter" cast.

Would Sir Ian McKellen, best known for his role as Magneto in the "X-Men" franchise, have been a better choice as the Hogwarts headmaster? Hello Giggles reported that he was, in fact, considered for the role.

He wasn't the only one who could have joined the "Harry Potter" cast but ended up not passing up the chance.

According to What Culture, Kate Winslet was the first choice to play Helena Ravenclaw. However, she never got a chance to consider it because her agent allegedly rejected the offer because of "a rather snobbish view on Potter's prolificness."

Kenneth Branagh was a huge hit as Gilderoy Lockhart, but he was only the second choice for the role. Hugh Grant already agreed to and signed on for the role but he had to let it go because of scheduling conflicts.

Rosamond Pike delivered an amazing performance in "Gone Girl," but would she have been amazing as the sleazy Rita Skeeter? Unfortunately, she said no and the part went to Miranda Richardson.

The same situation happened to Naomi Watts when her agency refused the casting offer for Narcissa Malfoy. Thankfully, Helen McCrory gave an amazing performance as Draco's mother and Lucius' wife.

Another big shocker is the casting for Sybill Trelawney. Although Emma Thompson was great, some people still wonder how the sometimes-seer would have been portrayed if Tilda Swinton took the role instead.

In the eyes of a "Harry Potter" fanatic, Alan Rickman should never be replaced with someone else as the tragic Severus Snape. So it would come as a surprise for some that Tim Roth was initially tapped to play the potions master. However, he jumped ship to Tim Burton's "The Planet Of The Apes" even before filming started.

The late Robin Williams also had to pass up the chance to play Hagrid because he wasn't British. The same issue came up with Liam Aiken's initial casting as Harry Potter himself.

Nevertheless, the existing "Harry Potter" cast did help make the series one of the film industry's biggest franchises to date.