The Papilio protenor is commonly known as the Spangle, a swallowtail butterfly of the Papilionidae Family, first published in 1775.
The male Spangle is a velvety indigo-blue black, duller on the fore wing than on the hind wing. The female is similar in color, however slightly lighter in shade with no indigo on the fore wing.
See more information on the Spangle at Wikipedia.
The Spangle pictured below was rather unfortunately caught in the web of a Golden Orb Weaver.