Dragon Quest: The Adventure of Dai (Japanese: DRAGON QUEST –ダイの大冒険–, Hepburn: Doragon Kuesuto: Dai no Daibōken; lit. "Dragon Quest: The Great Adventure of Dai") is a Japanese manga series written by Riku Sanjo and illustrated by Koji Inada, based on the popular video game franchise Dragon Quest. It was serialized in Shueisha's Weekly Shōnen Jump from October 1989 to December 1996, with its chapters collected in 37 tankōbon volumes.

A prequel manga series began in V Jump in September 2020 and a spin-off manga began in Saikyō Jump in October 2020. The manga was adapted into an anime series, produced by Toei Animation and broadcast on TBS from July 1991 to July 1992. It is the second anime adaptation based on the Dragon Quest franchise after Dragon Quest: Legend of the Hero Abel. The manga received a second 100-episode anime adaptation by Toei Animation, which was broadcast on TV Tokyo from October 2020 to October 2022.

Dragon Quest: The Adventure of Dai is one of the best-selling manga series of all time, with more than 50 million copies in circulation by 2022.

The story begins with a young boy named Dai remembering a story told to him by his adoptive grandfather, the monster magician Brass, about the defeat of the Demon King Hadlar by the hands of a hero known as Avan. After the defeat of the Demon King Hadlar, all of the monsters were released from his evil will and peace reigned supreme around the world once again for ten years. Some monsters and demons moved to the island of Dermline to live in peace. Dai, the young protagonist of the series, is an orphan and the only human living on the island. Having been raised by Brass and with his best friend, the monster Gome, Dai grows up dreaming of becoming a hero.

After Dai befriends Leona, the princess of the Kingdom of Papnica and saves her from peril, Avan comes to the island accompanied by his apprentice, the magician Popp, to become Dai's teacher by her request. However, his training is interrupted by the return of Hadlar, who was resurrected by the Great Demon King Vearn and became the commander of his vast army. Avan sacrifices himself to protect his disciples and Hadlar is temporarily driven away by Dai after he awakens a mysterious power within himself.

To honor Avan's final request, Dai, Popp and Gome leave the island and begin their quest to defeat Hadlar and his master to bring peace back to the world. During their travels, Dai's party gains three other members; the healer Maam, who later also becomes a martial artist, Hyunckel, one of Hadlar's former subordinates, and Leona herself. Their enemies include Beast King Crocodine, an honourable but ruthless commander of Hadlar's army, the Mystic legion commander Zaboara and his son Zamza, a magical elemental of ice and fire known as Flazzard, the illusive Mystvearn, who himself is a greater servant of Vearn and is Hyunkel's teacher of black magic, Killvearn, a jester who is Vearn's personal assassin, and Baran, a legendary warrior and Dai's father who sided with Vearn after the death of his wife and the disappearance of his son.

After learning that it would take Yuji Horii three years to finish Dragon Quest IV, Weekly Shōnen Jump deputy editor-in-chief Kazuhiko Torishima had the idea to create both an original anime and original manga based on the video game franchise. When Horii could not do it himself, Torishima tapped Riku Sanjo to write the latter. Torishima would still have Horii supervise the manga to make sure it did not feel out of place in the Dragon Quest world. When the artist he originally planned to have illustrate the work turned it down, Torishima offered Koji Inada the job. Inada also initially turned it down as he was dead set on creating his own original series, but accepted when Torishima threatened to drop him if he passed on the job.

Although a one-shot, "Gush! Gulp!" (デルパ!イルイル!, Derupa! Iruiru!) was a two-part work, so Inada had to enlist help from his brothers and friends in order to finish it. The story reached between fifth and seventh place in the reader surveys and was followed by a three-part one-shot, "Dai o' Might!!!" (ダイ爆発!!!, Dai Bakuhatsu!!!). When this story reached number three in the rankings among popular series such as Dragon Ball, serialization was approved, and Dragon Quest: The Adventure of Dai began in Weekly Shōnen Jump in October 1989. Torishima left the project after reviewing the storyboards for the first three chapters.