Russia's ambassador to Sudan was found dead Wednesday in Khartoum. That's the seventh Russian diplomat to have died since November last year, in addition to an aide to a former deputy prime minister, a lawyer for a Putin-foe, and a former Russian MP. All but two died on foreign soil. Some were shot, while other causes of death are unknown. Note that a few deaths have been labeled "heart attacks" or "brief illnesses." Here's what you need to know:

You probably remember Russia's Ambassador to Turkey, Andrei Karlov — he was assassinated by a police officer at a photo exhibit in Ankara on December 19. On the same day, another diplomat, Peter Polshikov, was shot dead in his Moscow apartment. The gun was found under the bathroom sink but the circumstances of the death were under investigation. Polshikov served as a senior figure in the Latin American department of the Foreign Ministry. Russia's Ambassador to the United Nations, Vitaly Churkin, died in New York this past week. Churkin was rushed to the hospital from his office at Russia's UN mission. Initial reports said he suffered a heart attack, and the medical examiner is investigating the death, according to CBS. Russia's Ambassador to India, Alexander Kadakin, died after a "brief illness" January 27, which The Hindu said he had been suffering from for a few weeks. Russian Consul in Athens, Greece, Andrei Malanin, was found dead in his apartment January 9. A Greek police official said there was "no evidence of a break-in." But Malanin lived on a heavily guarded street. The cause of death needed further investigation, per an AFP report. Malanin served during a time of easing relations between Greece and Russia when Greece was increasingly critiqued by the EU and NATO. On the morning of U.S. Election Day, Russian diplomat Sergei Krivov was found unconscious at the Russian Consulate in New York and died on the scene. Initial reports said Krivov fell from the roof and had blunt force injuries, but Russian officials said he died from a heart attack. BuzzFeed reports Krivov may have been a Consular Duty Commander, which would have put him in charge of preventing sabotage or espionage. Ex-KGB chief Oleg Erovinkin, who was suspected of helping draft the Trump dossier, was found dead in the back of his car December 26, according to The Telegraph. Erovinkin also was an aide to former deputy prime minister Igor Sechin, who now heads up state-owned Rosneft. A lawyer for a Putin-foe, Nikolai Gorokhov, was reportedly thrown from a window March 21 in Moscow. However, press outlets with ties to Russian security forces reported Gorkohov fell while trying to move a bathtub into his apartment. Gorokhov was set to testify as a U.S. government witness in a money laundering case in New York. A former Russian MP, Denis Voronenkov, was shot dead in Kiev March 23, according to the BBC. Voronenkov was to testify against deposed Ukrainian President Viktor Yanukovych and had ruffled feathers in Russia for calling the Crimean annexation illegal. Kiev police said it was likely a contract killing but the Kremlin rejected the remarks as "absurd." Russia's ambassador to Sudan, Mirgayas Shirinsky was found dead at his Khartoum home August 23. Per AFP he was found dead in the residence's swimming pool, although Sudanese police said he had died of natural causes. Russia's foreign ministry spokeswoman Maria Zakharova said embassy staff called an ambulance but he "could not be saved."

Some history: In November 2015, a senior adviser to Putin, Mikhail Lesin, who was also the founder of the media company RT, was found dead in a Washington hotel room according to the NYT. The Russian media said it was a "heart attack," but the medical examiner said it was "blunt force injuries."

Two cases that are a little clearer: In 2006, former KGB officer and whistleblower Alexander Litvinenko was poisoned with radioactive polonium. Six years later, whistleblower Alexander Perepilichny died from a toxin while jogging in England, per the NYT report.

Go deeper: BuzzFeed News has a team investigating a series of Russian-linked deaths (including Lesin, Litvinenko, and Perepilichny) well worth the read. Start with Part 1: "Poison in the System," here.