one of a kind #2

ロビン・ウィリアムズ氏の死去に際して、オバマ大統領が異例の追悼談話を発表しました。greenさん、ここの But he was one of a kind.とはどのような意味でしょうか。（UG）

Robin Williams dead; family, friends and fans are 'totally devastated'

President Barack Obama's statement sent from the White House summed it up:

"Robin Williams was an airman, a doctor, a genie, a nanny, a president, a professor, a bangarang Peter Pan, and everything in between.  But he was one of a kind. He arrived in our lives as an alien -- but he ended up touching every element of the human spirit.  He made us laugh.  He made us cry.  He gave his immeasurable talent freely and generously to those who needed it most -- from our troops stationed abroad to the marginalized on our own streets."

http://edition.cnn.com/2014/08/11/showbiz/robin-williams-dead/index.html?hpt=hp_t1