Ban Ki-moon used his final address to the General Assembly to unleash his outrage at leaders who have been supporting the five-year-long conflict in Syria.
"Powerful patrons that keep feeding the war machine also have blood on their hands. Present in this hall today are representatives of governments that have ignored, facilitated, funded, participated in, or even planned and carried out, atrocities inflicted by all sides of the Syrian conflict against Syrian civilians. Just when we think it cannot get any worse, the bar of depravity sinks lower."
But he singled out the Syrian government in particular for most of the atrocities committed.
"The conflict in Syria is taking the greatest number of lives and sowing the widest instability. There is no military solution. Many groups have killed many innocents, but none more so than the government of Syria, which continues to barrel-bomb neighbourhoods and systematically torture thousands of detainees."
The Syrian government has condemned Mr Ban's comments.
A Foreign Ministry statement says the UN, under Mr Ban, "has deviated from its role in finding just solutions for international problems."
It adds the international body has failed to resolve any conflicts during Ban Ki-Moon's leadership.
Turning elsewhere, Mr Ban accused South Sudan's feuding leaders of betraying their people, and criticised the Ukrainian, Palestinian, Israeli and North Korean leadership.
"In too many places, we see leaders rewriting constitutions, manipulating elections and taking other desperate steps to cling to power. Leaders must understand that holding office is a trust granted by people, not personal property. My message to all is clear: serve your people. Do not subvert democracy; do not pilfer your country's resources; do not imprison your critics."
The 72 year-old South Korean's term as Secretary General ends on December the 31st.
He says while he has much to be proud of, he has expressed his regret for sexual abuse by UN peacekeepers in Central African Republic and the UN's part in a cholera outbreak in Haiti.
Also addressing the General Assembly for the last time as United States President was Barack Obama.
Mr Obama used the moment to address several international disputes.
"It's a truism that global integration has led to a collision of cultures: trade, migration, the internet; all these things can challenge and unsettle our most cherished identities. We see liberal societies express opposition when women choose to cover themselves. We see protests responding to Western newspaper cartoons that caricature the Prophet Muhammed. In a world that left the age of empire behind, we see Russia attempting to recover lost glory through force. Asian powers debate competing claims of history. And in Europe and the United States, you see people wrestle with concerns about immigration and changing demographics, and suggesting that somehow people who look different are corrupting the character of our countries."
Canada's Prime Minister, Justin Trudeau, used his address to call on countries to learn from his country's resettlement of refugees.
"In recent months, Canadians have opened their hearts and their arms to families fleeing the ongoing conflict in Syria and from the moment they arrived, those 31,000 refugees were welcomed - not as burdens, but as neighbours and friends, as new Canadians."
