All death knights can summon ghouls. For those who lack the relevant talents in the Unholy tree, these are unnamed; they come in as "Risen Ghoul", last a couple minutes, and die. Unholy-specced death knights can make theirs last longer, or indeed permanently. (Well, until they get destroyed. Then it's time to summon a new one.) The names are chosen at random by matching A and B parts, and anyone traveling around death knights sees the patterns pretty quickly.
I do believe that there's a Firesign Theatre fan somewhere in Blizzard's staff, I must say: