Sheikh Saeed bin Tahnun Al Nahyan was the ruler of Abu Dhabi, one of the Trucial States which today form the United Arab Emirates (UAE), from 1845 to 1855.^[1]

Saeed acceded following the murder of his uncle, Sheikh Khalifa bin Shakhbut Al Nahyan. The murder led to a period of fighting for the leadership of the Bani Yas, with Sheikh Khalifa's maternal nephew and murderer, Isa bin Khalid al-Falahi attempting to take power but being himself killed by Dhiyab bin Isa. Khalid bin Isa then murdered Dhiyab and fled to Sharjah, leaving two influential leaders of the Bani Yas, Mohammed bin Humaid and Rashid bin Fadhil, to remove a claimant to the fort of Abu Dhabi, one of Khalifa's brothers, and nominate a son of the former leader Tahnun bin Shakhbut Al Nahyan, Saeed bin Tahnun.^[2]

Saeed arrived in Abu Dhabi to a smooth accession, supported by his two influential sponsors as well as approved of by the British. He quickly moved to quell a disturbance among the formerly secessionist Qubaisat and brought them to Abu Dhabi, stripped their boats and compelled them to pay their debts, return to the rule of Abu Dhabi and additionally pay a fine.^[2]

Saeed also moved on Buraimi, capturing his two forts back from the Wahhabis with the help of both the Dhawahir and Awamir tribes. He then pulled together the Bani Qitab, Ghafalah, Awamir and Bani Yas in Khatam and placed the Manasir and Mazari Bani Yas in Dhafrah to block the relieving Wahhabi army under Sa'ad bin Mutlaq. By 1850, Saeed's great tribal association had cleared Burami Oasis of Wahhabi forces. He subsequently accepted a stipend from the Sultan of Muscat for the defence of Buraimi.^[3]

Saeed bin Tahnun played a significant role in the Battle of Mesaimeer, a conflict that occurred in Qatar from June 2-4, 1851. This battle was fought between Qatari-Bahraini forces, led by Mohammed bin Thani and Ali bin Khalifa Al Khalifa, and the invading army of Faisal bin Turki, Imam of Emirate of Nejd. At this time, Qatar was considered a nominal dependency of Bahrain, and Faisal bin Turki was attempting to stage an invasion of Bahrain from the peninsula. Ali bin Khalifa, the Bahraini representative in Qatar, made overtures towards Saeed requesting assistance, and again wrote to him on 18 May, 1851, stressing the need for immediate reinforcements as Faisal's forces were a mere two days away from Al Bidda. Saeed obliged his request and rendezvoused with Ali bin Khalifa in Al Bidda.^[4]

Heavy gunfire was exchanged on 2 June near Al Bidda between the allied and Wahhabi forces, with the allied forces successfully repelling the initial invasion. On 3 June, the forces of Ali bin Khalifa and Saeed retreated to their ships and observed the ensuing close-combat skirmishes between Qatari and Wahhabi forces from sea. On the final day of battle, Faisal's forces retreated to their camp in Mesaimeer. Shortly after the final day of battle, Mohammed bin Thani sent a letter to Faisal's camp requesting peace and agreeing to be his subject, to which Faisal obliged.^[5] On 8 June, Qatari forces assumed control of Burj Al-Maah, a watchtower guarding Al Bidda's main water source, close to Al Bidda Fort where the allied forces of Ali bin Khalifa and Saeed were stationed. Upon hearing the news, they fled to Bahrain without incident.^[6]

Following the battle, tensions remained high between the various factions. Saeed, who maintained cordial relations with both the Bahraini rulers and the Qatari leadership, emerged as a key mediator in the ensuing diplomatic efforts. His involvement was prompted by concerns shared with other rulers of the Trucial Coast, particularly the Sultan of Muscat and the Sheikh of Sharjah, regarding the potential threat posed by Faisal's prolonged presence in Qatar.^[7]

In the third week of July 1851, Saeed arrived in Al Bidda (modern-day Doha) to facilitate negotiations. Working in conjunction with Ahmed bin Mohammad Sudairi, the chief of Al Ahsa, he successfully brokered a peace agreement by 25 July. The terms of this accord included:^[7]

• Ali bin Khalifa of Bahrain agreeing to pay an annual zakat of 4,000 German krones to Faisal bin Turki.
• Faisal pledging to restore the fort of Al Bidda to Bahraini control.
• A commitment from Faisal to cease interference in Qatari affairs.

Saeed personally traveled to Bahrain to secure Mohammad bin Khalifa's ratification of the agreement. His diplomatic efforts were crucial in de-escalating the conflict and restoring a measure of stability to the region. The successful mediation led to Faisal's departure from Qatar on 26 July, 1851, the lifting of the Bahraini blockade of Qatif and Al Bidda, and the withdrawal of British naval forces from the area.^[8]

In 1855, Saeed bin Tahnun was embroiled in a dispute involving the murder by a tribal elder of his^[whose?] own brother. The murder was considered not without justification but Saeed was deaf to the imprecations of the Bani Yas and resolved to have the killer put to death. A promise was made to the man of forgiveness, but when he was brought into Saeed's presence, Saeed drew out his own dagger and killed the man. The resulting violent uprising drove Saeed to take refuge first in his fort and then to exile on the island of Qish.^[9]

Saeed was succeeded by Sheikh Zayed bin Khalifa Al Nahyan.