Matt Hardy
One of the legends of the business, Matt Hardy also left and returned to WWE a few times. Hardy was released from WWE in 2010, after publicly requesting his release as he was unhappy with his status in the company.
After wrestling on TNA, ROH, and several indie promotions alongside his brother Jeff, the two returned to WWE in 2017.
But it seems that his current run with WWE could come to an end as his deal with the company will be up in the next few months.
Alberto del Rio
Alberto del Rio is a former WWE Champion, having won the WWE Championship twice and WWE Heavyweight Championship twice, while also winning the Royal Rumble. He was released by WWE in 2014 because of "unprofessional conduct" but he then returned to the company a year later in 2015.
He was a part of The League of Nations faction, which was the most prominent phase of his second run in WWE, before being released in 2016.