Ian McKellen's wizard decision to spurn Tom Cruise

Ian McKellan was about to become Gandalf because he turned down the chance to star with Tom Cruise. Photo / AP

Sir Ian McKellen almost missed out on two of his most iconic roles, Gandalf and Magneto, because of Tom Cruise.

The British actor was up for a part in Mission Impossible II alongside the Hollywood star, but turned it down when he saw the script.

"They wouldn't let me see the whole script because I might have spilled the beans. I only got my scenes," McKellen told People.

"Well, I couldn't judge from reading just those scenes what the script was like. So I said no. And my agent said, 'You can't say no to working with Tom Cruise!' and I said, 'I think I will'."

It was a good thing he turned down the role as the very next day X-men director Bryan Singer offered him the role of Magneto and not long after that he was asked by Kiwi director Peter Jackston to play Gandalf in the Lord of the Rings and Hobbit movies.

As shooting for X-Men then ran behind schedule, McKellen pulled out of the Lord of the Rings role but Jackson decided he was worth waiting for and held off shooting until he was ready.

Singer also agreed to rush through McKellen's X-Men scenes telling him: "Well, you must do Gandalf. I'll make sure you get out in time."

It turns out that by the time McKellen had finished shooting X-Men, Mission Impossible II still hadn't started shooting because of delays so he would have missed out on both parts if he had agreed to take the part.

"If I had decided to do that, I wouldn't have been in X-Men and I wouldn't have been in Lord of the Rings," he said.

- AAP