Scathach

Scáthach (Scottish Gaelic: Sgàthach an Eilean Sgitheanach), or Sgathaich, is a figure in the Ulster Cycle of Irish mythology. She is a legendary Scottish warrior woman and martial arts teacher who trains the legendary Ulster hero Cú Chulainn in the arts of combat. Texts describe her homeland as Scotland (Alpeach); she is especially associated with the Isle of Skye, where her residence Dún Scáith, or "Dun Sgathaich" (Fortress of Shadows), stands. She is called "the Shadow" and "Warrior Maid" and is the rival and sister of Aífe, both daughters of Árd-Greimne of Lethra.

Scáthach's instruction of the young hero Cú Chulainn notably appears in (The Wooing of Emer), an early Irish foretale to the great epic Táin Bó Cúailnge. Here, Cú Chulainn is honour-bound to perform a number of tasks before he is found worthy to marry his beloved Emer, daughter of the chieftain Forgall Monach. The tale survives in two recensions: a short version written mainly in Old Irish and a later, expanded version of the Middle Irish period. In both recensions, Cú Chulainn is sent to Alpae, a term literally meaning "the Alps", but apparently used here to refer to Scotland (otherwise Albu in Irish). Cú Chulainn is sent there with Lóegaire and Conchobor, and in the later version also with Conall Cernach, to receive training from the warrior Domnall (whose hideous daughter falls in love with the hero and when refused, promises revenge). After some time, Domnall assigns them to the care of Scáthach for further training.

...
Wikipedia