Who was Kakashi before Team Minato?

Kakashi was a prodigy — the youngest person to become a chunin in Konoha's history, advancing through ninja ranks with mechanical efficiency. He was rule-following, precise, cold. His father Sakumo Hatake (the White Fang) had chosen comrades over mission once and was shamed into suicide for it. Kakashi internalized the opposite lesson: rules exist for a reason; follow them even when it costs you.

What happened with Obito?

On a mission to rescue Rin, Kakashi followed orders to complete the mission rather than save Obito when he was buried by rock. Obito survived — and donated his Sharingan to Kakashi before what they both believed was his death. The gift transformed Kakashi and also created an unpayable debt. When Obito eventually returned, corrupted, Kakashi had to reckon with having been given a gift by the person he'd failed.

Who was Rin Nohara?

Rin was their teammate — gentle, loyal, deeply caring. She was later made a jinchuriki (Isobu was sealed inside her) by enemies of Konoha, designed to be released inside the village as a weapon. To prevent this, she asked Kakashi to kill her. He couldn't do it. She stepped in front of his Chidori intentionally. Kakashi watched her die on his own attack.

How did these losses shape Kakashi's character?

Completely. They're the source of his apparent laziness (chronic depression and exhaustion), his lateness (visiting memorial stones), his protectiveness of students, and his absolute rule about never abandoning comrades. He built his entire teaching philosophy around not making the mistake he made on that rock cliff.

What is the Sharingan's significance in his story?

He can't turn it off — it drains chakra constantly. He keeps it hidden under his headband because using it has a cost. This is also symbolically important: Obito's gift is simultaneously a burden Kakashi carries every day. He is perpetually marked by what he lost.