Grevane was a big man with a long face, and pale, leathery skin, "as if he'd spent years in the blowing desert wind and sand without seeing the sun". His hair was grey and he wore sideburns. A scar put a permanent sneer to his lip. He had "narrow, yellow teeth and a crocodile's smile." He had a deep, resonant voice and spoke with a thick British accent. He corrects Dresden's grammar, and speaks in Latin when asking Dresden if he plans to murder him "in cruor gelidus" (in cold blood), indicating some level of intelligence.
Grevane was Kemmler's first student. The Capiorcorpus describes him as "a dog mourning his fallen master," implying he was fully loyal to Kemmler. His partner is Quintus Cassius, still under the alias of Liver Spots.
In the series
"A Fistful of Warlocks"
In "A Fistful of Warlocks", Grevane is a member of the Thule Society, and an apprentice of Heinrich Kemmler, fighting Anastasia Luccio in Dodge City. His magical powers are strong enough for Luccio to believe he's a White Council wizard. He survives the battle and Luccio hunts for the two dark wizards.
In Dead Beat, he and Quintus Cassius attempt to abduct Waldo Butters with a bunch of zombies. At that time he has the copy of Die Lied der Erlking. Harry Dresden happens to be there and helped Butters escape.
Later, Grevane attacks Harry Dresden's apartment with an army of zombies and this time captures Butters. Harry negotiates a trade to get Butters back. That's when Corpsetaker arrives with an army of specters and they face off allowing Harry, Thomas Raith, Butters and Mouse to escape.
He shows up at the Field Museum of Natural History just as Harry finds the The Word of Kemmler and takes it from Harry and leaves him alone with Quintus Cassius. On Halloween night, he had started the Darkhallow when Harry and Carlos Ramirez arrive to stop him. Carlos slices Greveane's throat with his sword and executes him with his gun.