Zombie master/doc

With the unique ability to transform normal zombies into more dangerous variants, the master is not to be taken lightly. They're somewhat more intelligent and act to preserve their reanimated existence: they often try to avoid direct conflict and hide behind other zombies. This makes killing them fast enough--before they turn a pack of normal zombies into a pack of spitters and shockers--difficult. Only fight when it's alone (unlikely, but possible), when you are able to handle many advanced variants at once, or if you've got high-powered gear and can strike it down at range.

One strategy to kill a zombie master is to toss explosives or grenades at them, as the explosion can go right through its bodyguards.