Both names "Duncan" and Smith are among Scotland's most common names. -To get a correct answer, I'd suggest a few more clues, profession, approximate period etc.
Duncan II of Scotland was born in 1060.
George Smith Duncan was born in 1852.
Duncan McIntyre was born in 1907, in Glasgow, Scotland.
Iain Duncan Smith was born on April 9, 1954.
William Duncan Smith was born on 1825-07-28.
Duncan J. D. Smith was born in 1960.
Charlotte Duncan Smith Graham was born in 1912.
Adam Smith was born in Kirkcaldy, Scotland.
Duncan Pow was born in 1980, in Dumfries and Galloway, Scotland, UK.
Iain Duncan Smith was born on April 9, 1954.
Duncan Flanning was born on April 5, 1930, in Aberdeen, Scotland, UK.
Haldane Duncan was born on July 25, 1945, in Edinburgh, Scotland, UK.