Who was hemlock acording to the Macbeth by Shakespeare?

Hemlock is not a "who", it is a "what". It is a plant related to carrots and parsnips and cumin and cilantro and parsley, but it is a deadly poison. It is the poison used to execute Socrates as seen in Plato's Phaedo. In Macbeth one of the ingredients used by the witches in their stew is "root of hemlock digg'd in the dark".