Jim Henson passed away years ago, and Steve Whitmire took over many of his roles, including Kermit the Frog:
Although The Muppets Celebrate Jim Henson was his first on-screen performance as Kermit, he considers The Muppet Christmas Carol to be his first real production as Kermit.
Frank Oz is still with us, but he has largely retired, and Eric Jacobson has taken on Fozzie Bear, Miss Piggy, Animal, and Sam the Eagle:
At 2001′s MuppetFest fan convention Jacobson made his Muppet debut secretly performing Miss Piggy welcoming the fans “live via satellite”. Jacobson made his first major Muppet production debut performing Fozzie Bear, Miss Piggy, and Animal for 2002′s It’s a Very Merry Muppet Christmas Movie. He took over the role of Sam the Eagle starting in 2005 with The Muppets’ Wizard of Oz.