The assassination of Andrei Karlov came after days of protests in Turkey over Russia's role in Syria.
The assassination, by a sharp-suited gunman shouting "Don't forget Aleppo", came after days of protests in Turkey over Russia's role in Syria and on the eve of a unprecedented meeting of the foreign ministers of Turkey, Russia and Iran on the conflict.
Here is what we know so far:
Dramatic footage showed the very moment the gunman -- dressed in a dark suit, white shirt and tie, shot at his target, who was at the opening of a Russian photography exhibition at an arts centre in Ankara.
The assailant is seen standing behind the ambassador as he is speaking and then swaggering around the exhibition waving his gun and pointing aggressively into the air.
The man shouts "Allahu Akbar" ("God is greatest") and then talks in Arabic about pledging allegiance to jihad in Arabic, the footage shows.
He then switches to Turkish, shouting: "Don't forget about Syria, don't forget about Aleppo. All those who participate in this tyranny will be held accountable."
The state-run Anadolu news agency said the gunman had been "neutralised" in a police operation inside the centre after a 15 minute shootout.
The gunman was identified by the Turkish interior minister as 22-year-old Mevlut Mert Altintas, who had worked in the Ankara anti-riot police for the last two-and-a-half years.
It was not known if he was on duty in the exhibition hall at the time and if not, how he managed to gain access carrying a weapon.
Ankara mayor Melih Gokcek speculated on his official Twitter account that the policeman may be linked to the group of exiled preacher Fethullah Gulen, who is blamed for the July coup aimed at toppling President Recep Tayyip Erdogan.
It is not yet clear whether the assassin was acting alone and no group has claimed responsibility.
But it will add further to jitters in Turkey, which has been rocked by a wave of deadly bomb attacks carried out by Islamic State jihadists or Kurdish militants.
The attempted coup has led to a massive crackdown on so-called Gulenists and opponents of the increasingly authoritarian president.
The slain ambassador, Andrei Karlov, was a veteran career diplomat who helped weather rocky ties between Moscow and Ankara.
Karlov, 62, was appointed to Ankara in 2013 at a time when the two countries were pushing to boost trade ties despite deep differences over the conflict in Syria.
Russia's foreign ministry spokeswoman Maria Zakharova described his killing as a "tragic day in the history of our country and our diplomatic service".
Before serving in Ankara, the bespectacled Karlov spent a large chunk of his career -- which stretched back to the Soviet period -- working on the volatile Korean peninsula.
The married father-of-one -- who spoke Korean and English -- served in the Russian embassies in both North and South Korea, before later returning to Pyongyang as Moscow's ambassador to the isolated Stalinist state from 2001-2006.
The shooting came on the eve of a crucial meeting between the Turkish, Russian and Iranian foreign ministers on the Syrian conflict.
And at the exact moment of the attack, Turkey's Foreign Minister Mevlut Cavusoglu was on a plane flying to Moscow for Tuesday's tripartite talks.
Moscow and Ankara remain on opposite sides of the conflict -- with Ankara backing rebels trying to topple Moscow's ally President Bashar al-Assad.
Protesters in Turkey have held Moscow responsible for rights violations in war-wracked Aleppo, with thousands massing outside the Russian consulate in Istanbul.
Diplomatic relations between Ankara and Moscow sank to their worst levels since the Cold War in November last year when a Turkish jet shot down a Russian war plane over Syria.
But relations have since warmed, with intense contacts in recent days that led to a deal for evacuations from Aleppo.
And both sides vowed that Monday's assassination would not harm ties, with Erdogan swiftly calling President Vladimir Putin.
"We will not allow this attack to cast a shadow on Turkey-Russia relations," the Turkish foreign ministry said.
"The crime that was committed is without doubt a provocation aimed at disrupting the normalisation of Russian-Turkish relations and disrupting the peace process in Syria," Putin said.