Who is Count Olaf from The Slippery Slope and what is their importance?

Count Olaf is the main villain (antagonist) in the book and throughout the series. His greatest desire is to obtain the Baudelaire children's fortune, and in this novel, he has kidnapped Sunny Baudelaire, while sending Klaus and Violet rushing down a mountain path in a wagon to their presumed deaths. He is shocked to find at the end of the novel that they had survived his attempt to kill them. Olaf is described as a cruel and thoughtless man, who is vain about his own intelligence and appearance.