#1 The Hacker

This is one mystery that WWE haven't put a lid on yet. The Hacker, who played a part in the Mandy Rose-Otis-Dolph Ziggler-Sonya Deville storyline, has vanished from WWE television for quite a while.
The Hacker's last post on social media was in the last week of May, and hasn't been shown on SmackDown as well.
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One Superstar who was linked closely with the hacker storyline and was reportedly the man behind the glitches on SmackDown was Mustafa Ali. Ali was rumored to have been moved to RAW from SmackDown, but that hasn't been confirmed yet.
It will be interesting to see if WWE brings back The Hacker at Extreme Rules, to play a part in a storyline. He could reveal a secret, as he did in the love triangle storyline on SmackDown, or even reveal his own identity.
WWE have to reveal to fans who The Hacker is and continue that storyline as it looked promising. Bringing it back at Extreme Rules could be a way to add some spice to the PPV and get fans talking about the show.