Thierry de Loos (alternatively, Dietrich von Los) was a Franco-Flemish nobleman who took part in the Fourth Crusade and afterwards became prominent within the Latin Empire.
[1] Thierry, with the other participants of the Fourth Crusade, which had been diverted from the Holy Land, took part in the Siege of Constantinople in 1203 and the sacking of the same city a year later.
In 1204 he led the troops of the Latin Empire that captured the blind ex-emperor of Byzantium, Alexios V Doukas.
His brother, Willans (Willeaume) de Looz, was also prominent at the battle, where he was killed commanding the Latin rearguard.
Also in 1206, Thierry de Loos was invested by the Latin government with the city and region of Nicomedia as a fief, with the title duke.