Outside the courthouse, he is one of the most powerful men in the Middle East, overseeing Israel’s military campaign in Gaza, its occupation of southern Lebanon and recent strikes in Syria.

As he stepped into a cramped and sweltering underground courtroom in Tel Aviv on Tuesday morning, Prime Minister Benjamin Netanyahu of Israel morphed into the defendant in Case 67104-01-20 — charged with bribery, fraud and breach of trust.

Eight years after the police started investigating him and four years after his trial began, Israel’s longest-serving prime minister was taking the stand for the first time to respond to accusations of corruption that have defined and disrupted Israeli public life for nearly a decade.

“Like everyone who is brought to the witness stand, you are charged with speaking the truth, the whole truth and nothing but the truth,” said Rivka Friedman-Feldman, one of three judges hearing the case.

An audience of roughly 100 journalists, lawmakers, government ministers and lawyers craned their necks to catch his response.

“I have waited eight years for this moment — to tell the truth, the truth as I remember it,” replied Mr. Netanyahu, gripping the sides of a wooden lectern as he stood to the left of the judges.