Doyle became Wolves' record signing when he made the £6.5million move from Reading last summer.
The Republic of Ireland international has been linked with moves away from Molineux after playing a major role in Mick McCarthy's side staying up as the lone forward in a 4-5-1 formation.
But Bull, the club's record scorer with 306 goals, believes any doubts about Doyle's future have now been removed after Wolves finished 15th in their first season back in the top flight.
Bull told BBC West Midlands: "Kevin Doyle is superb. He is so under-rated it is unbelievable. I think Wolves will now be able to keep hold of him as they are staying in the Premier League.
"There would have been doubts if we had gone down because a lot of teams were looking at him and you can understand why given the way he has performed. But I think he will be there - and part of the Wolves team for years to come."