English and, especially, Scottish. Via Latin and Greek from Hebrew Messiah, "anointed".
This has been a popular forename in Scotland, particularly in the period since the publication of John Bunyan's "Pilgrim's Progress" although it was not uncommon earlier. It is occasionally used as a synonym for Christopher. In Scotland it is more often used as a female name.
There are many spelling variations in the 1841 Census of Aberdeenshire. Details of the variations in spelling are detailed under the female variant of Christian [q.v.].
Note that many old documents and some later ones replaced the first five letters with the single letter X, e.g. Xtian. In the older documents a Latin masculine ending -us was normally added, giving Christianus or Xtianus, modified for Latin case endings.