Matilda (or Maud -- the French form of the name) was the daughter of Henry I of England, and his wife Maud/Matilda of Scotland, herself daughter of Malcolm III and Margaret, daughter of Edward Atheling.
She was christened Adelaide, but adopted the name of Matilda/Maud on her marriage to Henry V, the Holy Roman Emperor, in 1114, aged 12. The marriage was childless and after 11 years Henry died. She returned to England where her father arranged a new marriage for her, with Geoffrey of Anjou (nicknamed Plantagenent), he being all of 13 years old. They were to have three sons, Henry, who would later become Henry II of England, Geoffrey, Count of Nantes, and William, Count of Poitou.
Henry I selected Matilda as his heir, having no sons, and had the English baronage swear to support her. Unfortunately, when he died in 1135, Stephen of Blois was positioned just across the English Channel, and he rushed over, to Winchester, where he had a brother as bishop, and had himself declared king (he had a claim to the throne through his mother, William the Conqueror's daughter, Adela of Normandy; additionally, the English did not want Geoffrey of Anjou as king, and had no remembrance of a woman as Queen regnant).
For 3 years Matilda laid her plans and marshalled her resources. Then, in 1139, with the support of Robert of Gloucester, Matilda invaded. In 1141 she captured Stephen at the battle of Lincoln, and was on the point of making herself Queen (taking the title "Lady of the English") when the citizens of London rose against her and, soon after, Stephen wriggled free from his prison, swapped for Robert. A year later he was to beseige her in Oxford but (supposedly concealed within a white cloak to match the snow-covered countryside) she escaped. Their war went on until 1147, when Robert of Gloucester died, and Matilda returned to France, to govern Normandy, which Geoffrey had conquered from its duke.
However, her son Henry had grown into a fine man, and when, in 1153, Stephen's heir, Eustace, died, Henry crossed the Channel himself, and Stephen (perhaps by now wearying of his treachery) agreed, by the Treaty of Wallingford, that on his death Henry should succeed. He (Stephen, not Henry) lived but another year before God saw fit to end his nineteen year reign (which commentators cast as miserable and godless) and Henry took the throne, as England's first Plantagenet king.
His mother remained in France, and died in 1169, the daughter, wife and mother of Henry, as it were.