West Ham completed the signing of the former Manchester United man for a fee of £16m from German side Bayer Leverkusen on Monday and Sullivan was delighted to get the deal done.
"I think he is potentially the best player who has ever come to the club," explained the 68-year-old in an interview with 'talkSport'.
"In recent years, he is probably the best-proven goalscorer we have signed since we have been at the club."
"He's done it in the Premier League with Manchester United. We were lucky he only had a year left on his contract with his club and that allows you to negotiate a deal."
The former Birmingham City co-owner also revealed that West Ham came close to signing Hernandez when he left Manchester United two years ago.
"We tried very hard to get him two years ago but unfortunately he chose the German club ahead of us," said Sullivan.
Given his track record it would certainly seem like the Mexican is the perfect signing for the 'Hammers'. Who knows, could the Londoners' annual striker search be cancelled next year?