A variant of Alastair and Alexander, meaning defender of men.
Alaster is a variant spelling of Alastair or Alasdair, the Scottish Gaelic adaptation of Alexander — itself derived from the ancient Greek Alexandros, meaning "defender of men" (alexein, to defend + aner/andros, man). The name's journey from classical Athens through Roman conquest, Christian saints' calendars, and medieval Scottish Gaeldom is one of the great odysseys of European naming history. Alexander the Great (356–323 BCE) carried the name to the edges of the known world, and his legend was so powerful that the name became virtually universal across Western and Central Asia, adopted into Arabic as Iskandar, into Persian as the same, and into the Celtic languages of Britain as Alasdair.
In Scotland the Gaelic form Alasdair has been in continuous use for over a thousand years. It was borne by three medieval kings of Scotland — most famously Alexander III (1249–1286), whose reign was remembered as a golden age before the Wars of Independence. The name threaded through Highland clan histories, Jacobite poetry, and the diaspora of Scots emigrants who carried it to Canada, Australia, New Zealand, and the United States.
The spelling Alaster sits between the Gaelic original and the anglicized Alastair, preserving the old sound while sitting more comfortably in English orthography. Today Alaster is rare enough to feel genuinely distinctive while its phonetic cousins Alastair and Alistair remain in common use. It carries the full weight of the Alexander tradition — heroic, scholarly, regal — filtered through a specifically Scottish lens of literary romanticism and Highland pride. For parents drawn to Celtic heritage without the ubiquity of Liam or Finn, Alaster offers a name of considerable depth.