Step 1: The eponym Father of Toxicology is reserved for the scholar who first articulated that toxicity depends on quantity. That scholar is Paracelsus.
Step 2: His dictum that the dose alone decides whether a thing is a poison remains the cornerstone of the subject, earning him the title.
Step 3: A common trap is Orfila, who instead earns Father of Modern Toxicology for turning the field into a rigorous forensic science a few centuries later.
Step 4: Galen belongs to classical medicine and Galton to fingerprint and heredity studies, so both are unrelated distractors.
\[\boxed{\text{Paracelsus}}\]