"By hook or by crook" is an English phrase meaning "by any means necessary", suggesting that any means possible should be taken to accomplishing the goal. The phrase is very old, first recorded in the Middle English text Controversial Tracts by John Wyclif in 1380.
The origin of the phrase is obscure, with multiple different explanations and no evidence to support any particular one over the others. For example, a commonly repeated suggestion is that it comes from Hook Head in Wexford, Ireland and the nearby village of Crooke, in Waterford, Ireland. Another is that it comes from the customs regulating which firewood local people could take from common land; they were allowed to take any branches that they could reach with a billhook or a shepherd's crook (used to hook sheep).
Another theory is that the expression dates from the days of the first Norman invasions of Ireland, when rudimentary sailing boats left from Bristol or Pembroke bound for Ireland. The first Norman king of Ireland was Richard III. Back in his day, depending on the weather, the voyage to Ireland could be extremely hazardous and many ships didn’t make it. For the Normans, the two most extreme points on the Irish southern coast with harbours where they could possibly dock were Hook Head in Wexford to the east, and Crookhaven in Cork to the west. If you failed to make land between Hook and Crook, you were going off towards the wild Atlantic and the treacherous west coast, where the seas were huge, the ports few, and the native Irish not too friendly to the hapless Normans. Therefore, the Normans vowed to land in Ireland “by hook or by crook” and deploy any means necessary to do so, because to miss the stretch between Hook Head and Crookhaven meant the voyage was a total failure.