Macul Atum, known better by his Cerberus Daily News screen name "Hemlock", was a sociopathic volus chemist. Having a checkered path in ethically questionable research on Noveria, he was contracted by Obertian Turnonav to reverse-engineer the incredibly potent hallucinogenic drug LIGHT. Quite happily conducting experiments on live subjects dragged off of Omega's streets, he played lapdog to the batarian for several months.
He was later captured by investigators working at the behest of the STG, forced to recreate his findings, and was brought to Yomi with the other investigators, where he was eventually killed.
Hemlock formed part of the Who Goes There? story arc.