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Khalid ibn al-Walid ibn al-Mughira al-Makhzumi (Arabic: خالد بن الوليد بن المغيرة المخزومي, romanized: Khālid ibn al-Walīd ibn al-Mughīra al-Makhzūmī; died 642) was a 7th-century Arab military commander. He was undefeated in battle and is widely considered to be one of history's greatest and most successful military commanders. He initially headed campaigns against Muhammad on behalf of the Quraysh. He later became a Muslim and spent the remainder of his career in service to Muhammad and the first two Rashidun caliphs: Abu Bakr and Umar. Khalid played the leading command roles in the Ridda Wars against rebel tribes in Arabia in 632–633, the initial campaigns in Sasanian Iraq in 633–634, and the conquest of Byzantine Syria in 634–638.

As a horseman of the Quraysh's aristocratic Banu Makhzum clan, which ardently opposed Muhammad, Khalid played an instrumental role in defeating Muhammad and his followers during the Battle of Uhud in 625. In 627 or 629, he converted to Islam in the presence of Muhammad, who inducted him as an official military commander among the Muslims and gave him the title of Sayf Allah (lit. ' Sword of God '). During the Battle of Mu'ta, Khalid coordinated the safe withdrawal of Muslim troops against the Byzantines. He also led the Bedouins under the Muslim army during the Muslim conquest of Mecca in 629–630 and the Battle of Hunayn in 630. After Muhammad's death, Khalid was appointed to Najd and al-Yamama with the purpose of suppressing or subjugating Arab tribes who were opposed to the nascent Muslim state; this campaign culminated in Khalid's victory over Arab rebel leaders Tulayha and Musaylima at the Battle of Buzakha in 632 and the Battle of Yamama in 633, respectively.

Khalid subsequently moved against the largely Christian Arab tribes and the Sasanian Persian garrisons of the Euphrates valley in Iraq. He was reassigned by Abu Bakr to command the Muslim armies in Syria and he led his men there on an unconventional march across a long, waterless stretch of the Syrian Desert, boosting his reputation as a military strategist. As a result of decisive victories led by Khalid against the Byzantines at Ajnadayn (634), Fahl (634 or 635), Damascus (634–635), and the Yarmouk (636), the Rashidun army conquered most of the Levant. Khalid was subsequently demoted and removed from the army's high command by Umar. Khalid continued service as the key lieutenant of his successor Abu Ubayda ibn al-Jarrah in the sieges of Homs and Aleppo and the Battle of Qinnasrin, all in 637–638. These engagements collectively precipitated the retreat of imperial Byzantine troops from Syria under Emperor Heraclius. Umar then dismissed Khalid from the governorship of Jund Qinnasrin around 638. Khalid died in either Medina or Homs in 642.

He is generally considered by historians to be one of the most seasoned and accomplished generals of the early Islamic era, and he is likewise commemorated throughout the Arab world. Islamic tradition credits Khalid for his battlefield tactics and effective leadership of the early Muslim conquests, but also accuses him of illicitly executing Arab tribesmen who had accepted Islam—namely members of the Banu Jadhima during the lifetime of Muhammad, and Malik ibn Nuwayra during the Ridda Wars—and being responsible for moral and fiscal misconduct in the Levant. Khalid's military fame disturbed some of the pious early Muslims, most notably Umar, who feared it could develop into a personality cult.