7. Big Evil (2001 - 2003)
Technically, Undertaker's Big Evil era is just an extension of the American Badass gimmick (just with more of an emphasis on the "evil"). He still rode his motorcycle out to the ring, he still knew how to talk trash on the mic, and he even still had the same theme music for a while. The only difference was that he cut his hair and behaved a lot more ruthlessly.
The Big Evil persona saw 'Taker clash with the likes of Triple H, Stone Cold Steve Austin, and even Hulk Hogan (for the first time in a decade), bringing him his fourth WWE Championship in the process. It also saw him win the Hardcore Championship for the first and only time in his career.
The reason that the gimmick ranks ahead of the American Badass one is down to the fact that 'Taker himself was in a much stronger condition. Back in ring-shape and moving around the ring like he was 10 years younger, this period saw the beginning of an in-ring renaissance for The Phenom as he would produce some classics with Jeff Hardy, Brock Lesnar, The Rock and Kurt Angle.
It was great seeing The Undertaker back on top and that in-ring renaissance would continue to hit new strides even after he evolved his character again.