Botulinum toxin (commonly known as Botox) is a neurotoxic protein produced by the bacterium Clostridium botulinum, and it is considered the deadliest natural substance known, with an estimated lethal intravenous dose of just 1.3–2.1 ng/kg. It works by blocking the release of acetylcholine, causing flaccid paralysis—the hallmark of the disease botulism—and it was historically weaponized by Soviet, US, and Iraqi biological programs. Of the seven main toxin types (A–G), only types A and B cause human disease and are extensively used in medicine. When heavily diluted, it treats conditions like muscle spasticity (from stroke or cerebral palsy), strabismus, excessive sweating, and chronic migraine (FDA-approved in 2010). Major milestones include the 2016 FDA approval of abobotulinumtoxinA for pediatric lower-limb spasticity, and the 2025 resolution of the complete 14-subunit toxin complex structure. Despite its extreme lethality, its therapeutic applications have made it a revolutionary tool in both medicine and cosmetics.