Operation to kill al-Baghdadi named for Kayla Mueller — an ISIS hostage who refused to turn from Christ before her death

The operation during which Islamic State terrorist leader Abu Bakr al-Baghdadi was killed was named after Kayla Mueller, a humanitarian aid worker who was taken as a hostage in Syria and killed in 2015.

Mueller suffered brutal torture and rape at the hands of al-Baghdadi during her 18 months of captivity — but through it all, she never turned away from her Christian faith, according to ABC News.

American hostage Kayla Mueller was tortured, verbally abused, forced into slave labor for ISIS commanders in Syria and raped by the group's top leader, but her fellow hostages say she never surrendered hope, she selflessly put the welfare of fellow captives above her own and she even stood up to executioner "Jihadi John" to defend her Christian faith.

Mueller's faith was put to the ultimate test in the most dangerous and painful conditions possible. But according to those who were held captive with her, she boldly defended it to the British ISIS torturers they referred to as "The Beatles":

In March 2014, Mueller was taken to a room next door several times where male hostages were being held. Former hostages said Emwazi paraded her in front of them to show prisoners about to be released who she was and to offer her own proof-of-life by removing her head scarf and briefly introducing herself.

Former hostage Daniel Rye Ottosen, a Danish freelance photographer, recalled how Mueller turned the tables on the men in black.

"One of the Beatles started to say, 'Oh, this is Kayla, and she has been held all by herself. And she is much stronger than you guys. And she's much smarter. She converted to Islam.' And then she was like, 'No, I didn't,'" Ottosen told ABC News.

He admits it surprised him a lot. He had once tried to strangle himself when ISIS guards strung his arms up by chains.

"I would not have had the guts to say that. I don't think so," he said. "It was very clear that all of us were impressed by the strength that she showed in front of us. That was very clear."

In addition to the recollections of other former hostages, Mueller's trust in God was solidified through a handwritten letter the other captives delivered to her parents after they were freed.

"I remember mom always telling me that all in all in the end the only one you really have is God," Mueller wrote. "I have come to a place in experience where, in every sense of the word, I have surrendered myself to our creator b/c literally there was no else.+ by God + by your prayers I have felt tenderly cradled in freefall…I have been shown in darkness, light + have learned that even in prison, one can be free. I am grateful."

"I have come to see that there is good in every situation, sometimes we just have to look for it," she continued. "I pray each day that if nothing else, you have felt a certain closeness + surrender to God as well + have formed a bond of love + support amongst one another."

President Donald Trump announced al-Baghdadi's death Sunday morning, which was the result of a U.S. military special forces mission.

(H/T: FaithWire)

Editor's note: This article has been updated to correct the assertion that Mueller was working with Doctors Without Borders.