Brother of Tessa Dahl, Ophelia Dahl, and Lucy Dahl. His older sister, Olivia Twenty Dahl (b. April 20, 1955 - d. November 17, 1962), died from complications of the measles at the age of seven (when Theo was two).
Suffered a brain injury at four-months old, when his baby carriage was struck by a taxi. The most serious of his injuries was Hydrocephalus (commonly known as water on the brain). His father, author Roald Dahl, got together with a pair of friends -- a neurosurgeon and an engineer -- and created a device called the Wade-Dahl-Till valve to alleviate cranial pressure. The device allowed Theo and others suffering from Hydrocephalus to recover from their injuries.
