Feanor and sons

Then Feanor swore a terrible oath. His seven sons jumped to his side and took an oath with him, and their drawn swords shone blood red in the light of the torches. They swore an oath like ours is allowed to break it and our swear it, in the name of Ilúvatar himself, and they called the Eternal Darkness upon themselves when they did not hear it; and, calling Manwë to witness, Varda and the holy mountain Taniquetil, they vowed, with hatred and vengeance to the end of the world, to every vala, demon, elf or unborn man, or creature, big or small, good or bad who set the time until the end of days, whoever received a Silmaril from their own possession, kept or kept safe. "
This oath later became the undoing of the Fenaor clan.

Art by me