Eren Kruger

The 'Owl', secret leader of the Eldian Restorationists infiltrated in Marley's secret police: holder of the Attack Titan, he entrusts it to Grisha on the borderline and orders him to go into the Walls.

Kruger has passed himself off as a Marleyan for decades. On the borderline, after letting the other Restorationists be condemned, he transforms, kills the soldiers and throws officer Gross to the Titans; then he tells Grisha to marry and have children inside the Walls, because you don't need to save the world to love someone. He mentions 'Mikasa and Armin' to him — names he could not have known, except from memories of the future.