Here's why Eren Kruger adopted the persona of “The Owl” in Attack On Titan. Hajime Isayama’s Attack On Titan manga and Wit Studio’s anime focuses on a society that lives in settlements surrounded by giant walls put in place to protect them from Titans – a race of giant humanoids that roam the land devouring anyone they come across. Attack On Titan follows Eren Yeager who joins the military to fight the Titans and – like his fellow countrymen – believes his society is home to the last remnants of humanity.
However, Attack On Titan eventually reveals that what Eren and his people have been told is a lie: they are members of a nation known as Eldia that was responsible for the creation of the Titans and used them to establish a powerful empire that persecuted countries. One of those subjugated nations was Marley, which eventually overthrew Eldia and took control of several of its Titans. Most of the Eldians retreated to the nation’s last remaining territory Paradis Island where they built the walled settlements Eren Yeager lives in, while other Eldians were allowed to live in internment zones within Marley’s borders.
One of the Eldians left behind on the Marley-controlled mainland was Eren Yeager’s father Grisha. Like his fellow Eldians, Grisha was often on the receiving end of ill treatment from the ruling Marleyan people and his anti-Marley sentiments grew after his sister was murdered by its military. This led Grisha to join a resistance cell known as the Eldian Restorationists that sought to overthrow Marley and had a mole within its government known as “The Owl” who provided them with weapons and intel. “The Owl” in Attack Of Titan is, of course, Eren Kruger.
Like Grisha Yeager before him, Kruger was an Eldian born to a family living in Marley and his father was an Eldian Restorationist who was burned alive by Marleyan authorities for his rebel activities. Kruger nabbed a position in the Marley military while secretly acting as a spy for the Eldian Restorationists under the pseudonym of “The Owl.” He also has something of an intertwined history with Grisha, as he accosted him and his sister they day she was murdered and his military colleague Gross was responsible for her death.
Eren Kruger and Grisha Yeager were eventually reunited when Grisha and his fellow Eldian Restorationists were sent to Paradis Island to be transformed into Titans for treason. Kruger was one of the Marleyan military members overseeing the deportation and saved the life of Attack On Titan's Grisha’s by feeding Gross to the Titans. Kruger revealed his identity as “The Owl” to Grisha and his actions clearly had an impact on the Eldian rebel, who went on to name his son and Attack On Titan protagonist Eren Yeager after the man who saved his life.