Big Al is a name of an Allosaurus, a large carnivorous dinosaur who lived in the Late Jurassic around 145 million years ago.
'Big Al' is the name given to a real Allosaurus fragilis skeleton which was found near Howe Quarry in the Morrison Formation of North America in 1991. The skeleton was unusually well preserved - over 95% of his bones were found - and they were all in the same positions as when he had died. He measured about 8 meters (26 feet) in length. Nineteen bones were broken or showed signs of infection, which probably contributed to Big Al's death. This completeness of his skeleton gave Big Al his name. In fact, in terms of size he wasn't big at all - he wasn't even fully grown.
He was featured in the BBC's Walking with Dinosaurs series in the "Ballad of Big Al".