"having the qualities of a dog" (mostly in a negative sense), c. 1300, from dog (n.). Meaning "persistent" is from 1779. Hence doggedly (late 14c.), "cruelly, maliciously;" later "with a dog's persistence" (1773). Related: Doggedness.
1. He has been dogged by allegations of questionable business practices.
2. His career has been dogged by bad luck.
3. A dogged air of confidence exuded.
4. Their dogged single-mindedness is almost heroic.
5. I was quite impressed by her dogged determination to succeed.