I have noticed that Igneel is Natsu's foster parent, but to notice that his years with Igneel were quite short. Though the real question is to whom Natsu's real parents are and where he came from.
Might be Spoiler for anime viewer.
The background information about Natsu is very limited. As the story progress, it is revealed that the Natsu is actually Zeref's younger brother who died 400 yrs ago along with his father and mother and resurrected as E.N.D(Etherious Natsu Dragneel). Igneel, Natsu's foster father, teaches him sacred(Lost) dragon slayer magic and sent him in present(future for Natsu).
Natsu's parents are dead and doesn't have any role later on, so their information were not so important, that might be reason why they were never reveled. Natus came from past 400yrs ago.