That guy in the wheelchair seems different from the infected humans shuffling through the streets. Although we don’t see him clearly, a couple of things make him stand out. First of all there’s his transport. It’s doubtful that there are wheelchair-using zombies marauding around a vertically-focused, Victorian city. Their upper-body strength would be useless for wheeling themselves about, and access would be appalling. Also, those gas-lamps attached to his chair are a definite signifier of difference. In contrast to the zombies’ flaming torches, they’re pieces of technological illumination, immediately implying intelligence over their feral countenance. The same goes for the ornate, steampunk design of the chair itself.
And one more abstract point is the direction and editing of his presentation. He’s depicted as facing to the right. When the zombie procession appears in the next shot, it’s facing left, implicitly shuffling towards him. The ringing of a church bell during this sequence implies some manner of summoning ritual, immediately placing them in his thrall. On a related note, his relaxed arms imply that he isn’t pushing himself in the chair, probably meaning that a servant is nearby. It’s worth noting as well, that the droning regularity of the bell’s sound echoes the heavy, ominous string hits in the soundtrack, which kick in precisely as the wheelchair user gets his close-up. All of this screams that he is important. Also, he has a beard, and bad guys tend to have beards.