Where does “Dougal” come from?

Dougal is an English form of Scottish Gaelic Dubhgall, from Old Irish dubgall.

Ancestry of “Dougal”, step by step

Step	Language	Word	Meaning
1	Scottish Gaelic	Dùghall	—
2	Scottish Gaelic	Dùbh	—
3	Old Irish	dub	black; morally dark, dire, gloomy, melancholy;...
4	Proto-Celtic	dubus	black
5	Proto-Indo-European	dʰewbʰ-	deep
6	Proto-Indo-European	dʰewh₂-	smoke; mist, haze

Dougal — Etymology, Origin & Word History | Etymology Explorer