... was an Anglo–Norman nobleman, whose invasion of Ireland in 1170 initiated the opening phase of the English conquest. His father, Gilbert FitzGilbert – the 1st Earl – had the same nickname, which may (according to Wikipedia) be a mistranscription or mistranslation of 'Striguil'. This is the name that was used from the 11th century until the late 14th century for the port and Norman castle of Chepstow, which is now in Monmouthshire. It was also applied to the Marcher lordship that controlled the area in the period between the Norman conquest and the formation of Monmouthshire in the 16th century.
This question probably owes its popularity to the fact that the name was borrowed by H. P. Bulmer Ltd. of Herefordshire, for a brand of cider that it introduced in 1962. Bulmers has an Australian website dedicated to this product, which states that "Strongbow was the name given to Richard de Clare, one of England's greatest knights of the 12th century. De Clare was the 2nd Earl of Pembroke, but was primarily known for his association with Dublin, Ireland. Dermont McMurrough, the King of Leinster, called on de Clare to help him defend his title against other Irish Kings. De Clare's army drove invaders from Dermont's territory. He was nicknamed 'Strongbow' for relying heavily on archers during these campaigns."
Wikipedia disputes this account of how De Clare got his nickname, on the grounds that (as stated above) his father, the 1st Earl, had the same nickname.
© Haydn Thompson 2019