Karim Khan, the International Criminal Court prosecutor who announced on Monday that he would apply for arrest warrants for leaders of Israel and Hamas, has gained a reputation over a long career in international law as a gifted speaker and a tough-minded litigator.
A British litigator, he took over as chief prosecutor of the I.C.C. in June 2021. Before that, he had served for both the defense and the prosecution at several international courts.
Among his high-profile clients were Seif al-Islam el-Qaddafi, son of the late Libyan dictator Muammar el-Qaddafi; and Charles Taylor, the former president of Liberia, who fired him.
One contentious case was his defense of William Ruto, now the president of Kenya, who faced charges of inciting violence that followed national elections. In 2016, when Mr. Ruto was deputy president, the case ended in a mistrial because of witness interference and political meddling. Mr. Khan was not accused of wrongdoing. He also worked on war crimes issues in Rwanda, Cambodia and Iraq.
The I.C.C. member nations elect a prosecutor in a secret ballot, and in 2021 they chose Mr. Khan after a monthslong deadlock. He received strong backing from Britain, among others in Europe. Though the United States is not a member of the court, Washington officials supported him behind the scenes.
One of his first acts as prosecutor, which took many by surprise, was to “deprioritize” an investigation into abuse of prisoners by American forces in Afghanistan, instead focusing on the larger-scale alleged crimes by the Taliban and Islamic State.
He began an investigation into Russia’s invasion of Ukraine soon after it began in 2022, and obtained an arrest warrant for President Vladimir V. Putin of Russia and another Russian official in March 2023. He had shown little progress in an investigation, opened in 2021, of alleged crimes by Israel against Palestinians, nor of crimes by Hamas.
Numerous legal commentators have argued that the disparity reflects a double standard that harms the court, though the court has said that the investigation has been hampered by lack of cooperation from Israel. Critics charged that Mr. Khan was slow to react to the Hamas-led attack against Israel on Oct. 7, and Israel’s subsequent military response, which has created a humanitarian crisis in its effort to crush Hamas.
But Mr. Khan has noted that investigators were allowed to work inside Ukraine immediately, while Israel has prevented him or anyone from his office from entering Gaza. He was recently permitted to travel to the West Bank and to villages in Israel that were attacked by Hamas.
Mr. Khan’s announcement on Monday that he had asked the judges for arrest warrants for two top Israeli officials — Prime Minister Benjamin Netanyahu and Yoav Gallant, the country’s defense minister — and three Hamas leaders was an exceptional event by I.C.C. standards.
Instead of waiting for judges to decide or sign warrants, he unexpectedly revealed his plans in a recorded announcement on the court’s website. Equally unusual was his simultaneous disclosure of a list of prominent experts, two of them former judges, whom he had consulted to review his evidence and his legal analysis before seeking the warrants. While prosecutors are known to consult specialists, some experts saw the publication of the list of names as an effort by Mr. Khan to demonstrate that there was strong legal support for his decision outside the court.
Christine van den Wyngaert, a veteran Belgian jurist who has served on the I.C.C. and other international tribunals, said Mr. Khan was “showing that he gave this a lot of thought.”
She added: “He appears to be more prudent than his predecessors. Their cases at times failed because they lacked sufficient evidence.”
