The tallest man on planet Earth ever was Robert Wadlow. He was born on 22 February 1918 in Alton state, Illinois, USA. He is also known as Giant of Illinois. He died at age 22. He reached incredible 2.72 m in height (8ft 11in), and weight of 220kg!
The reason for his great size lies in fact that he had abnormally high level of human growth hormone, more precisely he had hypertrophy of his pituitary gland. He never stopped growing, not even at age of 22. He died on July 15 1940, after an infection caused by irritation of his ankle.
Today, the tallest man on earth is Leonid Stadnyk from a small village Podoliantsi in Ukraine. He reached 8ft 5 in or 2.53 m! His condition is called agromegalic gigantism and he started to grow after a brain surgery which affected his pituitary gland. He was added to the Guinness book of Records at 27 September 2007.