Matilda (or
Maud) was the daughter of
Henry I, and after the death of his son
William Atheling in the
White Ship in 1120 she was the rightful
heir-presumptive to the
throne. However on Henry's death in 1135 his nephew
Stephen was persuaded to seize the throne. This led to
civil war.
Matilda's forces took London in 1141 and she was invested as Lady of the English. However, she was unpopular and had to leave later that year, and Stephen resumed the throne.
She was early on married to the Holy Roman Emperor Henry V (d. 1125), so was known as the Empress. Later she married Geoffrey Plantagenet (Count Geoffrey V of Anjou, d. 1151), thus initiating that dynasty in England, because the settlement in the civil war was that their son should succeed (as Henry II, sometimes surnamed Fitz-Empress) after the death of Stephen, which took place in 1154.
Her mother was Matilda or Eadgyth, daughter of King Malcolm III "Canmore" of Scotland and of St Margaret, the sister of Edgar Atheling (nominally King Edgar II after Hastings in 1066), so Matilda was the first of the Norman line to be an heir of the Saxon monarchy.
She died in 1167.