He didn't. He hasn't been a heel in at least 8 years.
2002-2003, then turned face and has been face ever since
He turned heel in 1998 when he joined forces with the Undertaker, then turned face in September 1999 He turned heel in April 2004 after Farroq retired and fueded with Eddie Guerrero
August 2004 after becoming the youngest world heavyweight champion, then betrayed Evolution no what u talking about evolution betrayed himm get ya facts straight. he turned heel when he challenged undertaker at wrestlemania.
John cena hhh christian undertaker sting if he comes Evan bourne rey mysterio and last but not least Yoshi tatsu
TNA management decided to turn him heel.
It is unknown whether John Cena will turn heel or not.
They turn face or heel by having a story line.
If you mean "heel" then no when you look at it undertaker never attacks anyone who doesn't deserve it in the eyes of the WWE universe so no he isn't.
no he will not jeff loves the fans and there's no prove that he will turn heel again
No. He has just been given more heel roles because of his menacing appearance.
I would have thought so.
It is not known if Rey Mysterio will ever turn heel. Many people have thought he has came close to turning heel.