From the Wikipedia entry on the biblical magi:
Traditions identify a variety of different names for the Magi. In the Western Christian church they have been commonly known as:
- Melchior (also Melichior), a Persian scholar
- Caspar (also Gaspar, Jaspar, Jaspas, Gathaspa, and other variations), an Indian scholar
- Balthazar (also Balthasar, Balthassar, and Bithisarea), an Arabian scholar
Caspar is also sometimes given as Gaspar or Jaspar. One candidate for the origin of the name Caspar appears in the Acts of Thomas as Gondophares (AD 21 – c.AD 47), i.e., Gudapharasa (from which 'Caspar' might derive as corruption of 'Gaspar').
Following on to the entry on the name Casper:
By the 6th century, the name Gaspar was recorded in mosaic at the Basilica of Sant'Apollinare Nuovo in Ravenna, Italy as one of the traditional names assigned by folklore to the anonymous Magi mentioned in the Gospel of Matthew account of the Nativity of Jesus. The letter "G" in the name Gaspar was clearly different than the letter "C" used elsewhere, suggesting that the name Gaspar preceded the name Caspar, and not the other way around as some have supposed.
The Western tradition of the name Gaspar also derives from an early 6th Century Greek manuscript, translated into the Latin "Excerpta Latina Barbari". A pseudo-Venerable Beda text, called "Collectanea et Flores", apparently continues the tradition of the name Caspar: "Secundus nomine Caspar" (P.L., XCIV, 541). This text is said to be from the 8th or 9th century, of Irish origin. As a surname, Gaspar survives today in Spanish, Portuguese and French, although the latter adds a silent d. It also survives in the Armenian name, Gasparian.
It would thus appear that the variants have a long history in Europe and would have followed British colonists, prisoners, etc. to Australia.