Ken Jennings kicked off his stint as interim host of the famous game show by honoring the man who made it famous ... saying Alex was pretty much perfect at what he did for more than 36 years.

Jennings pointed to Trebek's intelligence, charm and grace as reasons why he will never be replaced ... but told the audience the best way to honor him is "by playing the game he loved."

Jennings will be hosting throughout January to help the show out while it looks for a permanent replacement. Ken's obviously known as the greatest "Jeopardy!" contestant of all time, but when it comes to his hosting chops ... he's previously made it clear, "There will only ever be one Alex Trebek."

"Jeopardy!" paid its final respects to the beloved host last week with a 90-second video tribute thanking him for his 37 seasons of service, since he began the gig in 1984. The highlight montage played during the airing of the last episode Trebek taped.

In Trebek's heartbreaking final sign-off, he thanked viewers for watching and said he'd see them again next week. Sadly, Alex died 10 days later without filming another episode.