Discreet but influential - and hand-picked to his role by Prime Minister Benjamin Netanyahu - Avichai Mandelblit has become the first attorney general in Israeli history to indict a serving premier.

Standing in front of two Israeli flags, the grey-bearded 56-year-old struck a solemn tone on Thursday as he read out bribery, fraud and breach of trust charges against Netanyahu.

He said the decision to indict was made "with a heavy heart but with a whole heart."

Born in Tel Aviv to a right-wing family, Mandelblit is an Orthodox Jew and has six children.

He was nominated as attorney general by Netanyahu in 2016, and could become responsible for bringing down the country's longest-serving premier.

Well respected and quietly influential, he served under Netanyahu as cabinet secretary until 2015, working alongside the premier on a daily basis.

Before stepping into government roles, he was a senior lawyer for the Israeli army.

In 2004, he was named as chief military advocate general and promoted to general five years later.

In that strategic post, he was criticised by right-wingers for conducting investigations against Israeli soldiers suspected of abuses during a 2008-9 war in Gaza.

In 2014, after he had left the army, he was implicated in the so-called Harpaz affair, named after an officer convicted of producing false documents to influence the appointment of the army's chief of staff.

The investigation into Mandelblit was dropped, with no indictment brought.

Target of anger

Mandelblit has faced a near impossible challenge as attorney general.

The role stipulates that he represent the government in all legal cases and work alongside Netanyahu.

Yet shortly after the attorney general took office, the Israeli police detailed their suspicions over three cases, the most serious of which involves Netanyahu allegedly offering to change regulatory policies in exchange for favourable coverage from a media outlet.

He therefore faced the task of deciding whether or not to charge his "boss."

The case has made him a target of anger for many Netanyahu supporters.

Announcing his much anticipated decision Thursday, Mandelblit said it was a "hard and sad day" for Israel to indict a leader.

"The citizens of Israel, all of us, and myself, look up to the elected officials, and first and foremost to the prime minister," Mandelblit said.

"Law enforcement is not a choice. It is not a matter of right or left. It's not a matter of politics."

Refusing to answer questions or give interviews, Mandelblit remains an enigma for many commentators who speculate on his political inclinations.

But after being thrust into the spotlight, the world is now aware that the unassuming figure has become one of Israel's most important decision makers.