It’s hard to be the best at anything over a span of 28 years, let alone the precarious job of managing a mutual fund that invests in stocks.

It’s also a good way to introduce Ed Owens, who has overseen the giant Vanguard Health Care Fund since its inception in May 1984. Owens and his fund have been the very best-performing US stock fund over a very long haul.

Vanguard Health Care has earned an average annual return of 16.3 percent over those years, not only tops among US equity funds but much more than the Standard & Poor’s average annual gain of 11 percent, according to Morningstar Inc., the fund research firm.

One more important fact: Those gains produce a total return approaching 7,073 percent, compared with a return of less than 1,800 percent for the S&P 500.

Owens, 65, last appeared in this space eight years ago, on the occasion of his 20th anniversary running Vanguard Health Care. At the time, I called him the city’s best mutual fund manager you probably don’t know.

I talked to Owens yesterday because he is getting ready to retire as a partner at Wellington Management Co., the Boston firm that manages the $22.4 billion fund for Vanguard. Longtime associate Jean Hynes will take over the fund when he retires at the end of the year.

The story behind the Owens record isn’t flashy. Vanguard Health Care has been managed from the start as a value-oriented fund that kept portfolio turnover low and avoided big investment mistakes.

“It was kind of a boring strategy at any one point in time,” Owens said. But steady results compounded into top-ranked returns over years.

Look closer to see how a boring conservative strategy earned big money: Since 1997, Vanguard Health Care lost ground in only three years. It recorded two blockbuster years (earning 60 percent in 2000 and 40 percent in 1998) but otherwise produced solid annual gains over that period.

Good timing also factored into the Vanguard Health Care record. Health stocks were taking a beating when the fund was launched in 1984, and Owens had the early opportunity to buy cheap shares before the industry rebounded.

It’s probably not a coincidence that two other health funds based in Boston — Eaton Vance Worldwide Health Sciences and Fidelity Select Health Care — also rank among the best 10 performing US stock funds over the 28-year Owens era.

Vanguard Health Care did score some big hits in its stock portfolio along the way. The fund made a bundle shortly before its fifth anniversary when Sterling Drug, the maker of Bayer aspirin, was acquired by Eastman Kodak.

Owens later bought a big stake in Immunex Corp. after a drug failure sent the stock tumbling. Immunex fended off one takeover offer before eventually agreeing to be sold to Amgen Inc. in 2001. Owens estimates his fund earned about $1 billion on Immunex shares — a huge profit on a percentage basis — in less than a decade.

“That went on to be a 50- or 60-bagger for us,” he said. “It gave us an important boost in the second half of the ‘90s.”

Over time, Vanguard Health Care became a very big sector fund. (It manages about 10 times as much money as Fidelity Select Health Care.) That kind of bulging size tends to work against portfolio managers trying to outrun the market and fund competitors.

Owens says his fund’s focus on low stock turnover makes it easier to handle so many billions of dollars. However, over the past five years Vanguard Health Care has been a middle-of-the-pack performer. Its portfolio emphasizes big drug stocks such as Merck & Co., Forest Laboratories Inc., and Pfizer Inc. Meanwhile, health care funds that have performed better tended to focus more on smaller biotechnology companies, many of which have appreciated dramatically over those five years.

Owens may be retiring in a few months, but he didn’t hesitate when asked where he saw the big health care investment opportunities ahead.

“I think over the next 10 or 15 years, most of the growth is going to come from oncology,” he said. Also, “the biggest untapped market we have is Alzheimer’s, which is just waiting for the right product.” Recent clinical results for potential Alzheimer’s treatments have been disappointing, but Owens believes research targeting the disease will succeed in years ahead.

But Owens will be out the door long before that. He’ll take the best record in a competitive industry with him.