Killian is an anthropomorphic cougar and one of Varian's assistants. He has golden brown fur, cream muzzle, paws, feet, and muzzle, brown eyes, a spiky black head tuft. He wears a natural white, long-sleeved shirt with puffy sleeves and a high collar. On top of that he has a detailed dark teal vest with golden buttons and trimming. He also wears baggy, dark teal pants held up by a black belt with gold buttons. He seems to have some sort of a pouch attached to his left upper pant. He has boots with different shades of grey and a few golden buttons. He uses a bow and arrows as his weapons of choice.

Killian is a talkative and highly active boy with a mind for explosions and fireworks. He is almost always hyper and ready for action. He is friendly, caring, and very helpful. However, his energetic ways can lead to him making rash decisions and normally destroys or at least interrupts team projects. He is a very fast runner and a well fit acrobat with good reaction time but has terrible stamina. This changes over time as he is seen running for longer nearing the end of season 3.

Killian and Varian are close friends and like to play and rough house with each other. 

Antigone and Killian are good friends and are shown to have feelings for one another.

Killian is good friends with Phineas but is shown to get annoyed with him whenever he plays a prank on him. Normally, he finds a way to get him back.

He is on good terms with the rest of his teammates.

Trivia:

Killian's name means warrior

He is the most agile member of the Tangles

Like his animal comrades, Killian doesn't wear an apron.

Like his fellow animal companions, Killian doesn't seem to inhabit PTSD from being captured and experimented on. However, they do have flashbacks of the event.