Upin & Ipin is a Malaysian animated television series created by Burhanuddin Md Radzi and his wife, Ainon Ariff and is produced by Les' Copaque Production, based in Shah Alam, Selangor. The series follows Upin and Ipin, a five-year-old twin brothers who is characterised by their abundance of energy, imagination and curiosity about the world. Both twins, who lost their parents while they are still a baby, lived with their older sister, Ros and grandmother, whom they called Opah at the fictional Kampung Durian Runtuh. The titular characters are voiced by Nur Fathiah Diaz for the first three seasons, and from season 4 onwards, both twins are voiced by Asyiela Putri, while supporting and additional characters are voiced by the series' production staffs and are referred by their first names. This is a list of characters that is first appeared in Upin & Ipin. Characters that was first appeared in Geng: The Adventure Begins, but did not appeared in Upin & Ipin, are not listed.

Upin and Ipin (real name Aruffin and Ariffin bin Abdul Salam) are five-year-old twin brothers who live in a house in Kampung Durian Runtuh with their older sister, Kak Ros, and grandmother, Opah. They had become orphans, as their parents died during their infancy. Upin was born 5 minutes earlier than Ipin, and therefore, he takes his role as Ipin's older brother seriously. Upin is smarter in computers and is a little scientist at home. Ipin is cuter and funnier than Upin and likes to eat fried chicken. Ipin also tends to often repeat one word three times in one sentence, especially "Betul, betul, betul!". The twin brothers always act spoiled towards Opah, and like to tease their sister. Upin and Ipin attended Tadika Mesra.

Upin and Ipin is depicted as a baby in "Mimpi Terindah" and as an adult in "Upin & Ipin Dah Besar?". In the latter and "Tumbuh Rambut", both of the twins seems to have their hair grown up. The twin brothers imagined themselves as a clock in "Aku Sebuah Jam", as a pencil in "Aku Sebatang Pensel", as a book in "Aku Sebuah Buku" and as a car in "Aku Sebuah Kereta". The twin brothers also imagined themselves as a marine life in "Teroka Lautan" and as a cactus in "Tanya Sama Pokok". They are voiced by Nur Fathiah Diaz from seasons 1 to 3 and Asyiela Putri from season 4 onwards.

To distinguish the twin brothers, Upin has a spiral-shaped hair (his hair style resembles Laa Laa's antenna in Teletubbies) on his head and always wears a yellow tank top with the letter U written on it. Meanwhile, Ipin has no hair, also wears a blue tank top with the letter I written on it, and always wears a red cloth around his neck.

Kak Ros or simply Ros (real name Nur Roselia binti Abdul Salam) is the older sister of Upin and Ipin. Although she looks fierce and strict to her twin brothers, Kak Ros is a loving sister, and always plays with or teases her younger brothers. In addition, Kak Ros always teaches Upin and Ipin to be good, noble and thrifty. In the episode "Hari Misteri", Ros once gave a gift of a book entitled Cara Menjadi Adik Yang Baik (How to Be a Good Younger Sibling) to Upin and Ipin.

Ros is depicted as a young girl in "Mimpi Terindah". She had a pen pal from Japan named Hideko in the episode "Sahabat Pena", where Ros received a Japanese-styled postcard from Hideko and tries to make a Japanese food to celebrate Hideko's arrival to Malaysia. In the episode "Jaga dan Hargai Mata", Ros was seen to parodying the Metro-Goldwyn-Mayer logo where she roaring like the lion, implying that she is very fierce like the lion in the Pada Zaman Dahulu comic book, which Upin and Ipin read together. She is voiced by Siti Khairunnisa Mohd Ruduan since season 8.

Opah is a grandmother of Ros, Upin and Ipin. She has a wise nature regarding worldly and religious matters. In some episodes, Opah has a talkative nature and sometimes an excessive attitude towards her grandchildren, especially Upin and Ipin. She is also known as Mak Uda, especially by older Kampung Durian Runtuh residents, and is voiced by Ainon Ariff since season 1.

Ehsan bin Azharuddin is one of Upin and Ipin's close friends and classmates in Tadika Mesra, named after a member of Upin and Ipin's production crew. He is known for his rich upbringing, stout body shape and thick black-rimmed glasses. As a class monitor at Tadika Mesra, he wears a red bow tie with his uniform. Ehsan brushes his teeth five times a day. Like Upin and Ipin, he imagined himself as a clock in "Aku Sebuah Jam", as a pencil in "Aku Sebatang Pensel", as a book in "Aku Sebuah Buku" and as a car in "Aku Sebuah Kereta". He also imagined himself in "Teroka Lautan". He is voiced by Muhammad Fareez Daniel Mohd Sharabuddin since season 4.