In his final year of eligibility, Edgar Martinez finally cracked the 75% threshold and entered the Hall of Fame. His hitting stats were more than good enough, so the major thing that held voters back was the fact he played primarily as a designated hitter.
That logic doesn’t seem entirely fair. By the time Martinez ever DHed in a game, the position had been around for 14 years. When he first appeared on the Hall of Fame ballot, it was a fully established baseball position.
It is fairly well known that Ron Blomberg was the first ever designated hitter.