The Rivalry: A classic case of sibling rivalry based on Thor apparently being their father Odin’s favourite son, while Loki lives in his brother’s shadow.
Darkest Moment: Not content with tricking Thor into acting against his father’s wishes and getting banished to Earth, he then tells the soon-to-be Avenger that their father Odin has died. Thor fails to see that his brother’s pants are on fire.
Kiss & Make Up? Sadly not. While their family bonds convince Thor that his brother can be a good person again, Loki has a lifetime of resentment to prevent him from ever making amends.