In the latest episode of The Walking Dead, Negan joined the Whisperers, but it all might be a front for him to get close to Alpha. In Negan, the Whisperers have gained a powerful ally - if he can be trusted. Negan is a ruthless murderer with valuable knowledge of what goes on inside the walls of Alexandria, after all, and he once successfully controlled the region Alpha seeks to take over.
After being a prisoner for several years, Negan was finally released from his cell - though the person who released him is still a mystery, it was believed to be Brandon, the son of a loyal member of the Saviors. Brandon caught up with Negan after he escaped Alexandria, but in the end, Negan killed Brandon and crossed the border into Whisperer territory where he encountered Beta (Ryan Hurst). In The Walking Dead season 10, episode 6, "Bonds", Negan asks to be made a member, but the Whisperers are wary of him. Beta believes him to be weak and someone unworthy of being a Whisperer, but Alpha (Samantha Morton) seems to recognize Negan's value. At Alpha's direction, Beta puts Negan through a series of vigorous tests before finally turning on him.
To everyone's surprise, Negan overcomes everything Beta throws at him and proves himself to Alpha. After kneeling, Negan is accepted into the Whisperers. Though Negan expressed admiration of the Whisperers and their tactics, it's quite possible that Negan's interest in being one of them isn't as sincere as it may seem, if the comics are anything to go by. In the comic book version of this story arc, Negan does indeed join the Whisperers, but he has an ulterior motive. During a conversation with Alpha, Negan betrays her and slits her throat. Negan leaves, and Beta takes over as the Whisperers' new leader. With Beta in charge, the Whisperers send their horde against the communities.
Of course, the AMC series doesn't have to follow the comics to the letter, which means that the show could have different plans for Negan. However, the direction that The Walking Dead has been taking Negan as of late could indicate that in this case, the show will follow the comics. Negan has showed signs that he's a changed man - or on his way to becoming one - so he could end up having a trick up his sleeve in order to defeat the one threat that all the communities are facing, thus ultimately proving himself to the people of Alexandria.
So, like his comic book counterpart, Negan may have a secret plan in place. Negan actually knelt down in front of Alpha as a show of allegiance, and this sort of loyalty feels uncharacteristic of someone like him, despite all the years he's spent in jail. As someone who lost everything to Alexandria and Hilltop, Negan has good reason for hating Alpha's enemies, but it remains to be seen if he hates them enough to throw in with the Whisperers.