Fifteen South Korean crew members have gone on trial over the deaths of at least 292 people, most of them school pupils, in a ferry disaster in April.
Captain Lee Joon-seok, 69, and three others face the most serious charge of "homicide through wilful negligence".
His lawyer said the captain had no power to stop the firm from overloading the ferry, and insisted he had not meant to cause the accident.
Many relatives of the victims were in court to see the opening of the trial.
The case has received feverish media coverage, leaving commentators suggesting that the defendants will struggle to get a fair trial.
Hahn Jee-hyung, a judge who acts as a spokesman for the court, pleaded with the public not to take their frustrations out on the defence lawyers.
"The state-appointed lawyers have taken on the case out of public interest and not of their own will," Hahn told reporters.
The trial will focus on Capt Lee and his crew's escape from the sinking ferry while hundreds of passengers remained trapped inside.
If convicted, Capt Lee and three crew members could be handed the death penalty, but observers say it is extremely unlikely it would be carried out.
Eleven other crew are being tried on lesser charges of criminal negligence and maritime law violations.
Analysis: Lucy Williamson, BBC News, Seoul
It feels to many in South Korea as if the 15 faces lined up in a Gwangju courtroom today have already been tried and convicted.
Even before divers had begun to bring up the bodies from the sunken ship, the Sewol's captain Lee Joon-seok and the other rescued crew members were targets for the country's outrage and shock.
Claims by the captain and his crew that they had tried to save their passengers before leaving the ship were dismissed by an angry public. An employee from the ferry company itself told me his colleagues on board "should have done more".
In his opening statement, Capt Lee's defence lawyer Lee Kwang-jae insisted his client had no intention to kill the passengers.
"It wasn't like he had a grudge against the children, so it's difficult to accept the prosecution's argument that he wilfully neglected the duty of rescue and escaped to save himself," he said.
A nationwide manhunt is is still going on for fugitive businessman Yoo Byung-Eun, who is believed to own the Chonghaejin Marine company that operated the sunken ferry.
The police have also arrested executives of the ferry operator and subsidiaries of the investment firm held by Yoo's family but they have yet to be brought to trial.
The coastguard, which is set to be broken up, is also facing investigation on charges of negligence in the course of the rescue operation.
And the political fallout continues, with President Park Geun-hye being forced to appoint a new prime minister after the previous incumbent resigned over the tragedy.
On Tuesday, she nominated former journalist Moon Chang-geuk for the post.
Mr Moon is expected to take charge of overhauling bureaucracy and reforming safety standards.
'Akin to murder'
The ferry disaster caused an outpouring of public anger, and there have been calls for severe punishment for the crew.
President Park Geun-hye condemned the conduct of some of the crew of the ferry, calling it "akin to murder" and promising that those responsible would be "punished severely".
The confirmed death toll has reached 292, with 12 passengers still missing.
Prosecutors say the ferry owner ignored safety warnings and allowed the ship to be overloaded.