#3 Rusev
Rusev was brought in because Vince McMahon doesn't seem to realize the cold war is over. He tried several 'Russian' wrestlers, such as Vladimir Kozlov, before he ended up with Rusev, who is technically from Bulgaria and not the Soviet Union -- which no longer exists anyway.
Nonetheless, Rusev had a great deal of heat, mostly because of his massive body and athletic ability. Fans were willing to boo him, because booing the foreign-born heel is what wrestling fandom is wont to do.
However, Rusev's wife Lana wound up working on the Total Divas program on E network. Once fans saw the playful, goofy, and downright likeable side of Rusev, they were no longer willing to greet him with boos. Rusev upped the ante by capitalizing on his reality television fame by using social media and coming up with the novel "It's Rusev Day!" concept and catchphrase.
WWE seems to have seen the light, and are pushing him as a babyface of sorts now, but they don't seem willing to push him to the main event as they did when he was an unstoppable 'Russian' brute.
Why he got cheers instead of boos: Rusev's sunny personality and likeable demeanour shines brighter than the chrome on the Russian tanks he used to ride to the ring. Once fans realized what the 'real' Rusev was like, it was curtains for his heel character.