SIU is the pen name of Lee Jong-Hui, a South Korean manhwa creator born on May 29, 1986. The pen name is often interpreted as an abbreviation for "Slave. In. Utero," though the creator has also used the online handle "inutero". He majored in art education in college before completing South Korea's mandatory military service, a period during which he filled ten sketchbooks with concepts that would later form the foundation of his most famous work.

SIU is best known as the sole creator, writer, and illustrator of the webtoon Tower of God, which he began publishing on the Naver platform in 2010. The series follows a boy named Twenty-Fifth Baam who enters a mysterious tower in pursuit of his friend Rachel, facing a series of tests and political conflicts across the tower's many floors. The webtoon achieved significant commercial and critical success, becoming one of the most widely read international manhwa. It is part of a broader fictional universe SIU calls the Talse Uzer Story, governed by a specific set of unchangeable laws and history. In addition to the main series, SIU has created related works within the same universe, including the prequel or side story Cloud Atlas in 2012 and a spinoff focused on the character Urek Mazino.

The original Tower of God webtoon was adapted into a thirteen-episode anime television series that premiered in April 2020, with SIU credited as the original creator. A second season began airing in 2024, covering the Workshop Battle arc, which was subsequently branded as Tower of God: Workshop Battle for its continuation. The anime adaptations were produced by Telecom Animation Film, with SIU serving as the source material's author rather than a direct production staff member. The series has also been released in print through the WEBTOON Unscrolled imprint beginning in 2021.

Within his creative practice, SIU is known for constructing an expansive narrative world with ambiguous character motivations and complex tests of morality and strength. He has stated that his artistic influences include long-running shonen manga series, which inspired his approach to serialized, character-driven storytelling. The scale of his fictional tower is deliberately immense, with each floor described as being approximately the size of the North American continent. SIU's work has been credited with helping to popularize the Korean webtoon format internationally, leading to increased global distribution and adaptation deals for digital comics.