Cal-141 was a female Spartan appearing in the Halo Legends episode, "The Babysitter". She died saving ODST O'Brien from a Brute Chieftain on their mission to assassinate an unidentified Prophet, a government official of the alien Covenant trekking on their Great Journey, which was to unknowingly kill all living organisms.
A three-man squad of ODST Helljumpers is sent on a mission to assassinate an unidentified Prophet. Their sergeant, Cortez, decides that the mission is too dangers for the elite Helljumpers to go on alone, so he assigns Spartan Cal-141 as sniper, replacing O'Brien, which was a blow to his ego, even though he knows of the legend about Spartans.
Cortez briefs them through their mission, which was for the Spartan to snipe the Prophet from far away, with O'Brien as backup in case something were to happen to the Spartan. This was to break up a supply chain and bring unrest to the Covenant.
Already before they land on their planet, one of the ODSTs meets an unlucky demise where his jump pod is sent crashing onto a planet from bouncing off of a random asteroid, and O'Brien unluckily lands in a swamp with his oxygen tank damaged from crashing through a cliff. The Spartan impressively throws the pod out of the swamp, and O'Brien starts complaining to them to stop throwing him around even though he was rescued.
To get to their rendezvous point, they must sneak their way past Covenant forces in a mysterious settlement with strange architecture. O'Brien steps on a twig which alerts a Brute, and O'Brien stops the Brute right before it assassinated O'Brien, saving the ODST's life again. Cal then fights the Brute in hand-to-hand combat, killing the Brute even without weapons, which is impressive even for a Spartan, considering it was a Chieftain with a Brute Hammer. The Spartan carries O'Brien to safety after dangling off a cliff from the force of the Brute's swing, which only makes O'Brien hate the mysterious Spartan even more, and his ODST peers tell him to shut up or else the Covenant may ambush them.
Now that the ruins area was cleared, they were able to get to their rendezvous point before the Covenant spaceship containing the Prophet landed. Cal has the Prophet perfectly aligned with her scope, but even in her scope, she notices that the Brute was about to assassinate O'Brien yet again.
She saves O'Brien, but this time fails to block the Brute's attack and the hammer smashes her helmet with so much force that she won't have much more time to live.
Dutch, one of the ODSTs, lands the killing blow on the Brute with his submachine gun, finally killing the Brute. In the end, Cal was killed in action from the Brute that she fought earlier, and before her death, she tells O'Brien to take the shot. He proves his skill at long last and snipes the Prophet, with the mission now being a success, but at the tragic demise of a Spartan that influenced O'Brien despite barely knowing her and only seeing her without her mask for barely any time at all. An ignorant marine then mocks the Spartan and the ODSTs aggressively throw their apples at him, as O'Brien shows remorse for the Spartan.
Cal-141 was classified as missing in action, presumably deceased, since it is unknown if she was left for dead or somehow rescued. Regardless, the Spartan's selflessness had a profound impact on O'Brien, who then started to view Spartans more humanely and honorably.
Cal-141 was quite a formidable Spartan with impressive skill, able to overpower a Brute Chieftain in hand-to-hand combat without taking that long, a feat most Spartans would struggle to accomplish. She is highly trained in all aspects of war, including stealth, sniping, combat, situational awareness, and dependability. She also possessed great physical strength thanks to her SPARTAN-II augmentations, acquired through intense training. While Spartans also possess enhanced durability, it was not enough to survive the swing of a big hammer at brutal, superhuman force.
United Nations Space Command