The trailer for the Halo TV series revealed a human among the upper echelons of the Covenant - most likely a traitor. For years there have been attempts to bring Halo - one of the Xbox console's most popular brands - to life on the big or small screen. The dreams of the Master Chief are finally becoming a reality in Paramount TV+'s Halo series, which will see the Master Chief go to war against the alien Covenant, with the fate of all life in the galaxy at stake. But not all his enemies may be alien.
The TV series has a different timeline, but the basic concept seems to be the same. In the Halo universe, the galaxy is threatened by a religious Covenant that binds several races of religious extremists together. They seek the power of the Halo rings - ancient weapons that they believe will allow them to transcend to a higher state of being, but that in reality destroy all life around them. The Covenant are zealots, led by a group of Prophets - but, surprisingly, the first Halo trailer showed a human being standing among the Prophets, presumably helping lead the Covenant.
In the game canon timeline, the Covenant considered the very existence of humanity to be a blasphemy against the Forerunners. It's possible their religious zealotry has been dialed down a little for the Halo TV series in order to make them a little more relatable - and they've allowed some humans to their ranks. There may be a loose parallel with Troy Denning's novel Halo: Silent Storm, in which the Master Chief confronted a group of Insurrectionists who believed humanity was doomed and attempted to the Covenant to survive. Although this group didn't fare well, the Covenant would subsequently learn humans were needed to manipulate Forerunner artifacts, so in the new timeline they could have decided to keep a few around.
In narrative , it would make sense to add humans to the ranks of the Covenant. The humans can serve as viewpoint characters, introducing audiences to the various alien races in Halo and helping explain the Covenant's goals. They would also serve to accelerate the plot; in the original Halo games, Earth's location was a closely-guarded secret, but human traitors would be able to guide the Covenant straight to it. The introduction of human traitors could serve as the catalyst to lead the Covenant to Earth, where they discover ancient devices left behind by the Forerunners to point them to the Halo rings.
The Halo trailer certainly seems to suggest this is a high-ranking member of the Covenant, because she is stood around the Prophets - the powerful beings who guide the Covenant, teaching other races their misguided lore. There's been some discussion about the political themes running through the Halo TV show, with comparisons to Game of Thrones; it's quite possible these comments are actually related to Covenant politics, not human. The Halo series promises to be a quite remarkable reinvention of the franchise's lore.