Grattius was a Jiralhanae serving aboard the Covenant cruiser, Rapid Conversion as an engineering officer. He was a part of Maccabeus Clan and was a veteran member of the crew. He was also one of the only witnesses of Maccabeus' death at the hands of Tartarus, and, after that, he was the one who gave Maccabeus' helmet to Tartarus, thus confirming Tartarus' leadership of the pack.