The New York Post said Donald Frangipani filed the $5 million lawsuit against the U.S. cable television network and "Real Sports" host Bryant Gumbel in Manhattan federal court this week.
Frangipani accused the series of being "grossly irresponsible" and employing "biased" reporting in its "Real Sports" segment "Forger's Paradise."
In the segment, viewers were told Frangipani was the ring's "authenticator of choice" and verified as real thousands of fakes, the Post said.
"I had an excellent reputation, and, all of a sudden, I lost it all," Frangipani told the newspaper.
The complaint said Frangipani looked at fewer than 500 items for the ring and dismissed about 60 of them as forgeries.
The lawsuit noted that nothing he authenticated for the group was ever proven to be fake and the complaint added that many of the items the ring sold were actually real.
The Post said phone calls to HBO and Gumbel seeking comment were not returned.
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