Olentzero (Basque pronunciation: [olents̻eɾo]) is a Basque Christmas tradition. According to Basque traditions Olentzero comes to town late at night on the 24th of December to drop off presents for children. In some places he arrives later, for example in Ochagavía – Otsagabia on the 27th and in Ermua on the 31st.

The name Olentzero appears in a number of variations: Onenzaro, Onentzaro, Olentzaro, Ononzaro, Orentzago and others. The earliest records give the name as Onentzaro and the name is most likely composed of two elements, on "good" plus a genitive plural ending and the suffix -zaro which in Basque denotes a season (compare words like haurtzaro "childhood"), so "time of the good ones" literally. This suggests a derivation similar to the Spanish nochebuena, but the origin of Onentzaro, corresponding to the old feast of the winter solstice, is older than that of Christmas (which historically replaced the festival of Sol Invictus in 380 under Theodosius I in the Roman Empire).

Other theories of derivation exist but are not generally accepted:

Benito Lertxundi is a Basque singer-songwriter born in Orio in 1942 (Spain). He is an acclaimed and veteran figure in Basque music, who spearheaded with other key figures its revival in the 1960s and following years, showing an especial commitment to Basque culture and matters in general.