EWoT:Myriam Copan was an Aes Sedai of the Green Ajah who was raised to the Amyrlin Seat in 754 NE.
When she was raised in 754 NE she was considered a weak Amyrlin. However, after she returned from a seemingly self-imposed retreat in 758 NE she seemed a new woman. She was then a strong Amyrlin, considered one of the strongest the White Tower has ever had. She was considered a successful Amyrlin with Egwene al'Vere stating centuries later that she wants to be just like Myriam.
The true story, however, is not widely known. This "retreat" was actually a kidnapping by a fifty-three year old Cadsuane Melaidhrin. Cadsuane captured her with the intent to make her a stronger Amyrlin. Over the two months she had her captured, she toughened the Amyrlin through many methods, including physical ones. When she returned, she deflected the accusations by implying that Cadsuane did nothing of the sort.
Notably, Myriam chose Sereille Bagand of the White Ajah as her Mistress of Novices, though the name of her Keeper of the Chronicles and her subsequent Ajah are unknown. Sereille served excellently in the same office also during the reigns of the two Amyrlins who succeed Myriam (a Brown and a Gray respectively) becoming legendary in this role.