The logo of the idiots
ONI are a stupid bunch of freaks who led humanity secretly during the Human-Covenant War. They are idiots, with each and every one of them being a complete doofus.
They attack their allies, kill war heroes, kidnap children, blow up planets and erase people's memories. All for the good of 'Humanity'. There isn't an ounce of Humanity in the whole of ONI.
They secretly run the UNSC, but during the Fall of Lord Hood, Terrance Hood seized control of ONI and used it to tighten his grip over humanity. After Hood's death, ONI was abolished along with the UNSC.