It was the transformation that amazed movie audiences.

Meryl Streep was incredibly convincing when she played British Prime Minister Margaret Thatcher in the movie The Iron Lady with her mannerisms, her hair, and her accent. It was all so true-to-life, that Meryl Streep won the Best Actress Oscar® in 2012.

Now, Thatcher's death is again turning the spotlight on Streep's portrayal. So, just how did she pull off the transformation?

A behind-the-scenes video shows the lengths Streep and her makeup people went to to get it just right.

In the video, Streep said, "I had courage to play Margaret Thatcher because she was an interloper, and I thought, 'Well, if she do it I can do it.' "

Streep effectively played two Margaret Thatcher's—the take-no-prisoners Prime Minister who transformed British society, and the Thatcher of later years, weakened and stricken with dementia.

One critic called Streep's resemblance to the real Thatcher "uncanny" and said her performance was "flawless." Another said her portrayal was "impeccable."

Streep paid tribute to Thatcher Monday, telling INSIDE EDITION, "I was honored to try to imagine her late life journey. I wish to convey my respectful condolences to her family and many friends."