Saint Gerlach was a 12th-century Dutch anchorite who lived in Valkenburg aan de Geul. Originally a soldier and brigand, he underwent a religious conversion following the death of his wife. This transformation led him to undertake pilgrimages to Rome and Jerusalem, where he spent seven years caring for the sick. Upon returning to the Netherlands, he lived a life of extreme asceticism, residing in a hollow oak tree and donating his wealth to the poor.