SEOUL, South Korea — The criminal trial of Lee Jae-yong, who controls Samsung, one of the world’s largest corporate empires, has riveted South Korea since it began last spring. Prosecutors have cast him as a mastermind bent on breaking the law to protect his family’s wealth and power. He says he is a detached leader with little knowledge of the inner workings of his own companies.

Now, his fate hinges on which narrative a judge believes.

Mr. Lee, Samsung’s de facto leader and the third generation of his family to run the sprawling conglomerate, on Friday faces a verdict in a blockbuster bribery trial. The accusations, which have already sparked the impeachment of South Korea’s former president, have shaken the economic foundations of a country long seen as one of the world’s most successful growth stories. Prosecutors suggest that Mr. Lee be sentenced to 12 years in prison.

Mr. Lee and his lawyers say that he is innocent — and that he did not know enough about Samsung or South Korean politics to commit the crimes he is accused of. While Mr. Lee guides strategy and hammers out global alliances, he has little involvement in day-to-day operations, according to Samsung.

The defense says prosecutors have not produced a smoking gun showing that he directly bribed anybody. That would put greater importance on Mr. Lee’s personality and management style: Is he a smart, savvy operator? Or a low-key, hands-off and potentially naïve manager?