Dr Lanyon: The Shattered Witness
Dr Lanyon starts as Jekyll's complete opposite - a conventional, practical doctor who dismisses Jekyll's experiments as "unscientific balderdash." He's described as hearty, healthy, and boisterous, representing traditional Victorian medicine and rationality.
Lanyon's dramatic transformation after witnessing Jekyll's change into Hyde shows the story's central horror. From being robust and confident, he becomes pale, aged, and traumatised, telling Utterson: "I have had a shock, and I shall never recover."
His inability to cope with what he's seen represents how the revelation of hidden evil can destroy even strong, rational people. Unlike Utterson, who maintains his loyalty despite the mystery, Lanyon cannot accept the truth and literally dies from the shock.
Thematic importance: Lanyon's breakdown shows that some truths are too terrible to bear. His fate warns us about the dangers of uncovering the darkest aspects of human nature - sometimes ignorance truly is bliss.