Kovarian

Madame Kovarian was a mysterious and psychotic woman associated with the religious movement known as the Silence, an academy of the Question, and of whom Amy Pond had recurring visions during travels with the Eleventh Doctor. She wore an eyepatch over her right eye.

Biography
Some time after Amy Pond's honeymoon, Kovarian arranged her capture and replaced her with a Ganger, so perfectly synched to the real Amy that she couldn't tell. Amy's real body was taken to Demons Run in the 52nd century. Kovarian watched over her through a hatch above the room she was being held in, while her Ganger lived out her life. This affected the Ganger's mind as she saw visions of Kovarian wherever she went, often hearing her comments on how the pregnancy was going and how her health was. (DW: A Good Man Goes to War)

The first time Ganger Amy saw Kovarian was when she appeared at the little girl's bedroom door at Graystark Hall Orphanage. She appeared in a hatch in the door, which instantly disappeared. Amy was startled and asked who she was, but Kovarian ignored her and said "No, I think she's just dreaming". When Amy entered, the room appeared to be empty, with no evidence of Kovarian or the hatch. (DW: Day of the Moon)

While asleep on a pirate ship, Amy was woken by a noise and saw Kovarian in a hatch that opened on the hull of the ship. The woman said, "It's fine. You're doing fine. Just stay calm" and vanished instantly, along with the hatch. (DW: The Curse of the Black Spot)

She was seen twice by Ganger Amy at an acid mining factory, the first time whilst Amy searched for Rory, though she did not speak. The next time Kovarian was seen, Amy was able to sense her coming appearance, and stared at the point on the wall where the hatch would open. When she mentioned her to the Doctor, he tried to reassure her by dismissing it as "time memory, like a mirage." (DW: The Rebel Flesh / The Almost People)

After her Ganger form was destroyed, Amy awoke to find herself full-term pregnant in an alien hospital, with Kovarian looking over her. She went into labour, with Kovarian cruelly instructing her to push. (DW: The Almost People)

After Amy's baby was delivered, Kovarian took her away and had a Flesh duplicate created to serve as a decoy to keep the Doctor off her trail. The duplicate was 'rescued' along with Amy by Rory Williams. During the battle with the Headless monks, Kovarian told the Doctor she was "privileged" to have fooled him twice in the same manner and disconnected the Flesh signal, disintegrating the duplicate. (DW: A Good Man Goes to War)

Kovarian later appeared at the Luna University circa 5123 to River Song and taunted her over her capture as a baby and her role in the death of the Doctor. With the help of The Silence and soldiers from the Church, she kidnapped River and forced her into an astronaut suit. River was taken to 22nd April 2011 and submerged under Lake Silencio to kill the Doctor. (DW: Closing Time)

Kovarian appeared again in the Area 52 pyramid, tied onto a chair. She informed them about the 'eye patches' that caused either extreme pain or death, not knowing that her very own eyepatch was also included. It somehow fell, and Kovarian pleaded Amy Pond to save her, but Amy decided not to, and re-applied the patch, leading to Kovarian's fate - her death. Amy remembers this at the end. (DW: The Wedding of River Song).

Her ultimate fate is unknown given that her death occurred in an alternate timeline which was subsequently negated.

Personality
Kovarian was a cruel, manipulative and sadistic woman who deeply hated the Doctor for reasons unknown. She was willing to use the Doctor's friends against him and kidnap an innocent baby. She claimed it was a privilege to fool the Doctor twice with the same trick and seemed to enjoy watching Amy struggle to push out her baby. Later she tortured Amy emotionally by kidnapping the real Melody Pond and leaving a Flesh duplicate in her place. Kovarian was very callous, showing little concern for her allies and dismissed Colonel Manton without a second thought, mocking him by calling him "Colonel Run-away". (DW: A Good Man Goes to War)

Behind the scenes

 * Kovarian was credited as "Eye Patch Lady" until the mid-season finale of series six, A Good Man Goes to War. Kovarian made appearances in all the stories in this first half besides The Impossible Astronaut and The Doctor's Wife. She appeared under various circumstances, only to Amy Pond, and always through a gap in a surface that subsequently disappeared. Her appearances acted as a story arc throughout these episodes and even with her name, little, if anything, was revealed about her.
 * Kovarian was to have a cameo in Night Terrors before the episode was moved to the second half of Series 6.