Ismail Agha Shikak (Kurdish: ئیسماعیل ئاغا شکاک, Îsmaîl Axayê Şikak), also known as Simko (Kurdish: سمکۆ, Simko; 1887–1930), was a Kurdish chieftain of the Shekak tribe. He was a warlord who controlled significant land and led thousands of Kurdish rebels who defeated the Qajar and Pahlavi armies on several occasions. He had also fought against the Ottomans and other foreign troops in Iran. He also led ethnic conflicts of Assyrians and Azerbaijanis. In 1930, he was assassinated by the government of Pahlavi Iran.

Simko was born in 1887 in Chahriq-e Olya, Chahriq Rural District, Salmas County, to Mohammad Agha Shikak, the son of Ismail Agha, who was the leader of the Awdoyi clan of the Shikak tribe. Ismail Agha died in 1816. The Shekak played a prominent role in local politics, occupying the districts of Somay, Baradost, Qotur, and Chahriq. His brother, Jafar Agha, later became leader of the tribe. In 1904, Qajar official Nizam-ol-Saltaneh invited Jafar Agha to Tabriz for negotiations, and swore on the Quran that he would not be harmed. However, it had been a trap, and Jafar Agha was killed by Iranian authorities in Tabriz. In 1907, his father, Mohammad Agha Shekak, went to personally ask Abdul Hamid II for revenge against Iran, although he was imprisoned in Istanbul and died in prison.

Simko became the leader of the Shekak tribe in 1905 after the death of his elder brother Jafar Agha.

Simko was married to the daughter of Seyyed Taha, the grandson of Sheikh Ubeydullah, who was also a Kurdish nationalist who was actively campaigning for the unification of Iranian Kurdistan and Turkish Kurdistan in an independent state.

Kurdish nationalism was first introduced to Iranian Kurds during the reign of Abdul Hamid II, where the Ottoman Empire made several attempts to annex Iranian Kurdistan while encouraging nationalism to convince Iranian Kurds to the rest of the Kurds, who lived in the Ottoman Empire. The Young Turk Revolution did not change the policy. The Ottomans briefly controlled Iranian Kurdistan on two occasions, in 1906 and World War I.

In 1906, the Ottomans captured Mahabad relatively easily due to the Kurds being Sunni. In 1908, a group of Kurdish nationalists approached the Russian consulate in Urmia and asked for assistance in expelling the Ottomans. Simko was the most prominent figure who approached the consulate. The presence of Ottoman troops in Iranian Kurdistan had challenged the powerful status of Simko, while the Kurds were divided into Pro-Ottoman and Anti-Ottoman factions. Simko visited the Russian consulate in Urmia again in 1911 and visited Russia in 1912. Simko attacked the Ottomans and caused significant damage. Illarion Vorontsov-Dashkov often gave Simko rank promotions, which the Ottomans protested to Sergey Sazonov, but achieved nothing as the Russian consul in Van stated that Simko "is someone that we need and we should support him, since his hatred toward the Turks is without limit. And that benefits us." In the Persian Constitutional Revolution, Simko turned against the Constitutionalists, who were largely urban Azeris, and without being invited, sent 300 horsemen to join Iqbal al-Saltaneh, the governor of Maku, against the anjuman of Khoy. Simko was rewarded with the position of sub-governor of Qotur District, which the central government confirmed despite Simko's constant raids. Prior to 1913, Simko sided with pro-Ottoman and anti-Russian Azerbaijanis, although he delivered one of them, who sought refuge with him, to Russia in 1913, after which the Russians convinced the other Shikak leaders to pledge allegiance to Simko. In 1913, Simko and Abdurrezak Bedirkhan established the first Kurdish school in Iran in Maku and asked the Russian Vice-Consul Chirkov in Urmia for support, which he gave. Simko gathered 29 children aged between 8 and 10, and assigned 40 of his men as guards. Simko had personally handwritten a letter of gratitude to the Russian Czar. In 1914, they attempted to open another school in Khoy but were opposed by the Iranian government. Abdurrezak Bedirkhan notably supported the Cyrillicisation of the Kurdish alphabet and saw Russian influence as better than Arabic, Turkish, or Persian. Simko and Bedirkhan fell out after Bedirkhan wanted to turn the newly established cultural house into an anti-Ottoman pro-Russian political party, with Simko opposing, claiming that killing a few Ottoman soldiers would not benefit the Kurds as much as the school would. In March 1914, Simko Shikak participated in the Bitlis uprising against the Ottomans, having sent support westwards to the Kurdish rebels. In May 1914, he attended a meeting with Abdürrezzak Bedir Khan. Simko claimed that "only a fool" could not see the need for foreign support for the Kurdish nationalist movement. In World War I, the Russians were expelled from the region after the Ottomans captured Urmia and Tabriz in December 1914. Simko then became an Ottoman ally and massacred hundreds of Armenians and Assyrians. However, when the Ottomans requested help against the British, Simko refused. The Russians returned shortly after and briefly imprisoned Simko in Tbilisi, after which he returned to Iran, again a Russian ally. When the Russians withdrew in 1917, Simko became a British ally, which meant having to tolerate Assyrians and Armenians, whom he despised. He frequently changed sides as he was willing to ally with anyone who benefitted the Kurds. However, Simko was paranoid and believed that the Assyrians wanted to establish a state in Kurdish lands and ethnically cleanse the Kurds. The alliance did not last long, as Simko invited Shimun XIX Benyamin, the secular and religious leader of the Assyrians, for negotiations in March 1918, where Mar Shimun and the majority of his delegation were killed and butchered. Simko sided with the Ottomans when they invaded Iran in summer 1918. Several historians, as well as Lady Surma, the sister or Mar Shimun, claimed that the Iranian government had organized the assassination of Mar Shimun, with Simko only having acted as the executioner. Others claimed that the Ottomans had paid him to kill Mar Shimun. However, there is no evidence that support these claims. Jointly with the Ottoman Army he organized the massacre in Haftevan in February 1915 during which 700–800 Armenians and Assyrians were murdered.

During the Ottoman withdrawal from the South Caucasus after World War I, many ethnic Kurdish soldiers and officers deserted from the Ottoman army and joined Simko, inspired by his nationalist goals. Despite deserting, they had brought the Ottoman equipment with them to Iran. They were paid generously by Simko and formed the bulk of the Kurdish rebels in Iran. According to Armenian sources, Simko and Seyyid Taha were in contact with the British and with Turkish nationalists in May 1919. The Turkish nationalists had mainly wanted Simko to block the proposed repatriation of Armenians to western Armenia, promising support in return. In a letter to the British consul-general of Tabriz, Simko denied the claims of the Armenian sources that he sought Turkish support. There were British and Iranian suspicions that a large contingent loyal to Mustafa Kemal Atatürk had supported Simko, proof of those suspicions was never found. There were Kurdish nationalists from Turkey who joined Simko. According to British travelogue CJ Edmonds who interviewed Simko in 1922, Simko hated Turks more than Persians.

In 1918, the Simko Shikak revolt began, aimed at establishing an independent Kurdish state. Nearing the 1920s, Simko grew increasingly nationalist. However, Simko was primarily considered a tribal leader, as he lived in a time when Kurds primarily gave their allegiance to their tribe and had no concept of unity for a national cause. Simko lacked administration, which made him less successful than his contemporaries Mohammad Khiabani and Mirza Kuchik Khan. Simko was a pioneer of Kurdish nationalism and was among the first to attempt to unite Kurds of various tribal affiliation for a national cause. His failure was primarily due to the lack of nationalism among Kurds. However, Kurdish nationalism rapidly grew during the Pahlavi era in Iran, which also coincided with the Kemalist era in Turkey where Kurdish nationalism was also growing. Eventually, Qazi Muhammad successfully united various Kurdish tribes and established the Republic of Mahabad. Qazi Muhammad's father was a close friend of Simko and accompanied him throughout the battles. Before the Republic of Mahabad, Simko had made Mahabad his capital. Many of the veterans of the Simko Shikak revolt participated in the Republic of Mahabad, including Amar Khan Shikak who succeeded Simko as tribe leader.