Warlock was a hallucinogenic drug that smelled like liquorice. It was also an alien intelligence that had bonded with a mushroom when it crashed in Russia. For years it looked for a way to escape from Earth. The intelligence finally succeeded when it encountered Vincent Wheaton. His ability to amplify emotion boosted their desire to go home enough for it to leave the planet. (PROSE: Warlock)
The Doctor kept some Warlock in a gold snuff box. (PROSE: Warchild)