#1 DORA

Dora had a lot of voice changes throughout its run. According to Dora Fandom Wiki, Kathleen Herles voiced Dora in the first four seasons. Then, she was replaced by Caitlin Sanchez for the 5th and 6th seasons. During the last episodes of the 6th season, Sanchez was replaced by Fatima Ptacek, who continued being Dora’s voice until Season 8.
#2 BOOTS

For the first four seasons of Dora the Explorer, Boots was voiced by Harrison Chad before being changed to Regan Mizrahi for Seasons 5 until 7. In Season 8, Koda Gursoy snagged the role and is the current voice actor of Boots.
#3 BACKPACK

Sasha Toro voiced Backpack for Seasons 1 to 4. Alexandria Suarez later replaced her for Seasons 5 to 7 and Sofia Lopez for Season 8.
#4 MAP

The Map is also one of the show’s main characters, and Marc Weiner voiced it throughout all seasons without any voice actor changes.
#5 SWIPER

Swiper, the main antagonist of Dora and her friends, had the same voice actor as The Map. Marc Weiner also voiced Swiper, but in Dora and the Lost City of Gold, Benicio Del Toro bagged the role.
#6 TICO

Muhammad Cunningham voiced Tico in the first season while Jose Zelaya replaced him for Seasons 2 to 4. In Seasons 5 to 6, Jean Carlos Celi snagged the role before being replaced by Oscar Hutarra for Seasons 7 and 8.
#7 BENNY

Benny the Bull was voiced by Jake Burbage for Seasons 1 to 4 and Matthew Gumley for Seasons 5 to 7. They were replaced by Aidan Gemme later on for Seasons 7 to 8.
#8 ISA

Isa the Iguana was voiced by Ashley Fleming in Seasons 1 to 4, followed by Lenique Vincent for Seasons 5 to 6. In Seasons 7 to 8, Skai Jackson bagged the role as Isa’s new voice actor.
#9 BIG RED CHICKEN

The Big Red Chicken was also one of the characters who did not have a voice actor change. Chris Gifford voiced it from Seasons 1 through 8.
#10 GRUMPY OLD TROLL

Chris Gifford was also the one who voiced the Grumpy Old Troll, and he retained his role throughout the whole series.
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References:
https://dora.fandom.com/wiki/Dora_the_Explorer_Wiki
https://www.behindthevoiceactors.com/characters/Dora-the-Explorer/Dora/
https://www.imdb.com/name/nm1141558/?ref_=nm_mv_close
https://www.imdb.com/name/nm2377684/?ref_=nm_mv_close
https://www.imdb.com/name/nm3262742/?ref_=nmmi_mi_nm