Ford Pinto
When Ford introduced it in the early ’70s, the Pinto was popular due to its low price, fairly nice design, and a long list of options. They equipped it with economical four and six-cylinder engines, and the overall quality of the car was decent. However, while engineering the car, Ford left out any protection for its rear-mounted fuel tank. The fuel tank was below the trunk and just behind the rear bumper (via Time Magazine).
On most cars, there is a strong cross-member that protects the fuel tank in case of a crash. However, the Pinto lacked this feature, which became apparent when people started getting killed in fiery crashes caused by leaking fuel tanks. The families of people killed or hurt in such incidents sued Ford, and eventually, the company spent millions settling the court cases.