|Died||1942 (aged 76–77)|
|Allegiance||Kingdom of Greece|
|Years of service||1884–1923|
|Wars||Balkan Wars, Macedonian Front, Allied intervention in Southern Russia, Asia Minor Campaign|
Konstantinos Nider (Greek: Κωνσταντίνος Νίδερ, 1865–1942) was a Greek Army officer, who rose to the rank of lieutenant general and distinguished himself during the First World War and the subsequent Asia Minor Campaign.
Nider was born in Missolonghi in 1865, the son of the military doctor Franz Xavier Nider, one of the many Bavarians who had come to Greece with King Otto. He entered the Hellenic Army Academy and graduated on 12 August 1887 as a second lieutenant of the Engineers. Subsequently, Nider served for eight years in the Austro-Hungarian Geodetic Mission to Greece, which laid the foundations of the Greek Army's own Geographic Service. Promoted to lieutenant in 1890 and captain in 1898, he was a member of the Greco-Ottoman boundary commission after the Greco-Turkish War of 1897, and was sent to France for further studies in 1903. Upon his return he was promoted to major and placed in the newly established General Staff, and then in the staff of the 3rd Infantry Division. In 1910–14, he served as head of the Personnel Office of the Army, and as chief of staff of the rear area and support troops during the First Balkan War. He was promoted to lieutenant colonel in 1911. In 1914 he was promoted to colonel and became chief of staff of the I Army Corps.
During the National Schism, he remained loyal to King Constantine I. However, as he was not marked as an ardent royalist, he remained in the army following the King's exile and the assumption of power by the king's rival, Prime Minister Eleftherios Venizelos, in June 1917. Venizelos' victory led to the immediate entry of the whole country into World War I on the side of the Entente.
In June 1917, Nider was given command of the 1st Infantry Division. In December 1918, he was given command of I Army Corps, which soon after participated in the Allied intervention in Southern Russia, fighting the Bolsheviks in the Crimea and Odessa. On 2 June 1919, he was appointed head of the Greek Army of Occupation for the zone around the city of Smyrna (Izmir). He held this post until December, when he returned to his duties as CO of I Corps, which formed part of the occupation force. From this position, Nider fought in the subsequent battles of the Greco-Turkish War of 1919–22 from the same post, until he was replaced in February 1922.
Following his replacement, Nider tended his resignation, but after the Greek defeat in Asia Minor in August 1922 and the overthrow of the royal government by Venizelist officers, Nider was recalled to active service on 21 September and placed at the head of the Army of Thrace until his resignation on 25 December 1923. He became Vice Minister of Military Affairs in 1925, and head of the Military Household of the President of Greece (at the time his former chief of staff, Theodoros Pangalos, who had become dictator in 1925) from April to August 1926, whereupon he retired from active service and public life. He died in 1942.