Why do lions live in groups? Why do male lions have manes? How do competing carnivore species co-exist with lions? I will address each of these questions using data from a nearly 50-year study of the Serengeti lions, showing that lion prides are essentially "gangs" that compete incessantly with their neighbours, that the lion's mane is an ornament that honestly indicates the male's "quality" and that subordinate species such as cheetahs and wild dogs respond in contrasting manners to the threat of lion attacks. I will also highlight the way that lions influence the distribution and abundance of their primary prey species.