The River Douglas is in Scotland. The name of the river is from the old Gaelic words for "black water".
People who lived near the river took it as their surname ("the people from Douglas") and it moved from being a surname to being a given name. Note that in the sixteenth century it was used for girls as well as boys, although nowadays it is exclusively masculine.
Note that you will not find the name Douglas in The Bible.
Douglas Shaffer's birth name is Douglas Paul Shaffer.
Douglas Spitzer's birth name is Douglas Bradley Spitzer.
Douglas Brinkley's birth name is Douglas G. Brinkley.
Alastair Douglas's birth name is Alastair Baird-Douglas.
Chip Douglas's birth name is Douglas Farthing Hatlelid.
Douglas Bank's birth name is Douglas Frank Bank.
Douglas commercial
Douglas Cowan's birth name is Douglas Vanderyerk.
Douglas Travis's birth name is Douglas Fink.
Douglas DuVal's birth name is Douglas Pescatore.
Buddy Douglas's birth name is Lowry Douglas.
Burt Douglas's birth name is Burton Douglas.
Dawn Douglas's birth name is Dawn A. Douglas.
Douglas Leon's birth name is Douglas Lon.
The name "Douglas" in Hawaiian is translated as "Kukeleka".
Douglas Cosgrove's birth name is Irwin Douglas Cosgrove.
Douglas Craik's birth name is Craik, Douglas Stuart.