He's a cunning, manipulative, and utterly ruthless villain who relentlessly pursues the Baudelaire orphans' fortune, employing a variety of disguises and schemes to try and steal it.
While other characters like the adults in charge of the orphans, the "volunteers", and even the mysterious organization known as "VFD" might play a role in the story, Count Olaf stands as the primary obstacle to the children's happiness and the central force driving the plot.