As you may expect, the Christie surname is related to various Christian names, and is popular in Scotland, Ireland (often spelled "Christy"), and England. Since we know absolutely nothing about our Christie line (consider this page a cry for help), it is anyone's guess where the name originated for us.
Robert Christie 1907 - Unknown (approx.)
My grandfather's birth certificate is more confusing than it is informative. It seems that my great-grandmother was confused (it was customary in the 1930s to give women in labour a combination of morphine and scopolamine) when they asked her the name of the baby's father, and so she gave the birth father's first name, but her own father's last name. The result was a birth certificate that named my grandfather Robert Christie, but named his father as Robert Trowbridge. To add to this confusion, she claimed Robert was a physician with his own private practice, but gave his age as 25 - unlikely, even in the 30s - and did not know where he currently lived, despite claiming to be married to him (she wasn't). After doing as much research as is possible with so little to go on, this is what I've concluded as most likely: Robert Christie was likely born around 1907, and spent much of his early life in Chicago. It is possible that he did work in the medical industry (a 1940 census shows a Robert Christie, laboratory technician, at a veteran's hospital) and that my great-grandmother simply exaggerated his status.
Robert and Marie's children:
Robert Christie, b. 1932
Sources:
Birth certificate of son
Robert Christie 1932 -
Robert, the aforementioned baby with the confusing birth certificate, was born in Illinois in 1932 to Robert Christie and Marie Trowbridge. He currently resides in Texas.