For the past two years British barrister Karim Khan has been fighting for justice for the victims of ISIS.
Under his tenure as head of the UN's ISIS war crimes unit, many Yazidis were finally able to bury their loved ones this year.
Last month, he told the UN Security Council his team had found "clear and convincing evidence that the crimes against the Yazidi people clearly constituted genocide".
Now, Mr Khan, 51, faces one of the world's toughest roles as he is sworn in as the next chief prosecutor of the International Criminal Court tackling war crimes.
Mr Khan, who cut his teeth as a top international defence lawyer, was an outsider for the nine-year role.
Originally from the northern English city of Wakefield, in west Yorkshire, his grandfather was a miner and his parents worked at the local hospital as a consultant and midwife respectively.
Despite his recent years in Baghdad championing the cause of victims and striving to build war crime cases against more than 150 ISIS fighters, his new role is expected to be his biggest challenge yet as he enters a political minefield.
Mr Khan will inherit ongoing investigations into hotspots such as the Palestinian territories, Afghanistan, Myanmar and the Philippines.
"He's inheriting far too many situations for the office of the prosecutor, there is no way they can investigate them all," Kevin Heller, professor of international law at the university of Copenhagen said.
Already short of resources, the International Criminal Court is dealing with 14 full investigations and eight preliminary examinations.
Mr Khan will be closely watched as he takes on investigations opposed by powerful, non-member nations such as Israel, the US and Russia.
"The newest investigations in terms of some of the parties to the conflict will be difficult if not impossible to investigate," Mr Heller said.
His predecessor Fatou Bensouda was sanctioned by former US president Donald Trump's government, which opposed her decision to examine war crime allegations in Afghanistan, including by US troops.
President Joe Biden lifted the sanctions but Washington still opposes the ICC's attempts to claim jurisdiction over US and Israeli military personnel.
"The sanctions were a bit of a wake-up call," said Kate Orlovsky, director of the Hague Office of the International Bar Association.
Building on the work of Fatou Bensouda
Mr Khan previously said he was “realistic” about the task ahead.
"It is important to be realistic about what the court can achieve," he told the Opinio Juris legal blog.
"The worst scenario would be trying to do it all and ending up doing nothing.”
The Australian Centre for International Justice called on Mr Khan to build on the work of his predecessor Fatou Bensouda.
In her final hours in office, Ms Bensouda asked judges to open an investigation into thousands of killings during the Philippines' war on drugs.
President Rodrigo Duterte has refused to co-operate and campaigners are urging Mr Khan to bring them justice.
Cristina Palabay, secretary general of human rights group Karapatan, is calling on Mr Khan's help in the Philippines.
"We strongly urge the ICC Pre-Trial Chamber to grant Ms Bensouda’s request,” she said.
“We call on incoming ICC chief prosecutor Karim Khan to pursue the investigation into the human rights crisis in the Philippines and to hold President Duterte and all officials involved in the drug war accountable for their crimes against the Filipino people."
Ms Bensouda said Mr Khan's priority should be to obtain support for the court from state parties and non-members. She urged him to remain unmoved by personal attacks, criticism and even praise.
"What we do in this office is critically important, history will judge us," she said.
Mr Khan faces both external and internal pressure at the ICC.
An independent expert review last year criticised a "culture of fear" in the prosecutor's office and called for reforms to improve the workplace environment.
Mr Heller said Mr Khan was the type of outsider the office required.
"You need a little creative destruction, you need turnover at senior positions, you need a new prosecutor with a new set of perspectives, you need to shake things up," he said.
For those who know him there is little doubt in their minds Mr Khan is the right man for the job.
British-based Ryan D’Souza, executive producer of the Nobody’s Listening project which highlights ISIS crimes against the Yazidis, worked closely with Mr Khan in the past.
"Karim is held in high regard by Yazidi activists and civil society groups," he told The National.
"He led the exhumation of mass graves and then stood shoulder-to-shoulder with genocide survivors as they buried their loved ones.
“He has helped the Yazidis in their long fight for justice and I have no doubt he will bring the same energy and determination to his new role in helping others to also get justice and closure.”