who is he?
He is an American actor and singer.
Jonathan Groff
Jonathan Drew Groff (born March 26, 1985) is an American actor and singer. 
who does the voice for kristoff in frozen Jonathan Groff
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Jonathan Groff [SEP] Introduction
Jonathan Drew Groff (born March 26, 1985) is an American actor and singer. A prolific actor on stage, screen, and television, Groff is the recipient of a Grammy Award and has been nominated for two Tony Awards. Groff rose to prominence in 2006 for his performance in the lead role of Melchior Gabor in the original Broadway production of "Spring Awakening", for which he was nominated for the Tony Award for Best Actor in a Musical. He returned to Broadway in 2015 to play the role of King George III in "Hamilton" and sang the song "You'll Be Back", a performance for which he earned a nomination for the Tony Award for Best Featured Actor in a Musical.