At least 10,000 people used the chatrooms, with some paying up to $1,200 (£1,000) for access.
Some 74 people, including 16 underage girls, were exploited.
A police committee took the unusual step of naming Cho Ju-bin, 24, after five million people signed petitions.
“I apologise to those who were hurt by me,” Cho said as he was led away from a Seoul police station on Wednesday.
“Thank you for putting a brake on the life of a devil that could not be stopped.”
He did not respond when reporters asked if he admitted the charges.
He is accused of abuse, threats and coercion, and of violating the child protection act, the privacy act and the s.e.xual abuse act.
How did the chatrooms work?
As reported by Quartz, customers paid to access the so-called “nth rooms”, where extorted content from underage girls was uploaded. Fees ranged from $200 to $1,200.
According to Korean newspaper Kookmin Ilbo, each of the eight “nth rooms” hosted videos from three to four girls who had been blackmailed by chatroom operators.
The girls were active on chat apps, or Twitter, and engaged in prostitution or sexting for money.
The chatroom operators contacted the girls, promising modelling or escort jobs.
They were then directed to a Telegram account where the operator extracted personal details which were used to blackmail them.