Appearance and AbilitiesEdit
Records regarding the appearance of Tetsuan are scant. Scraps of history imply that she was "plain" in her appearance though exceptionally strong in her ability to channel. She would have praised herself to be the second strongest Aes Sedai since the time of Caraighan Maconar till the arrive of Eldrene who pushed Tetsuan to the third place. Because in TWoTC Caraighan is described at level 3(+10) it can be guessed that Eldrene was at 4(+9) and Tetsuan at 5(+8).
Due to the loss of knowledge that accompanied the destruction of records during the Trolloc Wars, very little of Tetsuan's history is known to loremasters. Her region of birth and her surname have both been forgotten.
What is known about her is that she arrived at the White Tower as a novice in the years prior to the Trolloc Wars where she became acquainted with fellow novice Eldrene ay Ellan ay Carlan of Manetheren.
White Tower records imply that Tetsuan and Eldrene quickly emerged as rivals and that Tetsuan became jealous of Eldrene's overwhelming beauty and strength in the power.  Specific details of their adolescent animosity are unknown, though it is believed that because she had a "plain" appearance, Tetsuan bent all of her time towards her studies in an effort to become more prestigious than Eldrene but was never quite able to surpass her rival. Both were raised to full Aes Sedai around the same time, with both choosing the Red Ajah.
Soon after receiving her shawl, Eldrene departed the White Tower and returned to Manatheren, eventually marrying and bonding King Aemon al Caar al Thorin many years later and becoming his queen. Tetsuan is believed to have remained in the White Tower and to have somehow caused the marriage between Eldrene and Aemon, both for political reasons and also to keep away her rival from the White Tower. Nonetheless the marriage between the two was happy and they fell in love to each other.
Tetsuan's activities as a full sister are lost to time, though given the length of the Trolloc Wars her career surely spanned at least a couple hundred years.  What is known with certainty is that she eventually rose to prominent political power within the tower. Ultimately she was raised to the Amyrlin Seat circa 1200 AB and became one of the first sisters from the Red Ajah to hold the office. 
Historians relate that at this time Manetheren fell under siege by the forces of shadow. During this period King Aemon had answered pleas from allies in the Ten Nations and had overextended his military - a flaw that the shadow sought to exploit - and Aemon recalled his army back to his homeland when he realized that Manetheren was in grave danger.  Ultimately his forces clashed with the enemy in a titanic multiple day struggle that came to be known as the Battle of the Tarendrelle River. 
Knowing that his forces would be unable to repulse the Shadow alone, Aemon sent messengers to all the allied nations and a special plea was sent to Tetsuan. It is believed that when Tetsuan received Aemon's messenger she was influenced by her childhood hatred of Eldrene and selfishly chose to betray Manetheren by working to halt or delay responses from allied nations. Her actions ultimately led to the annihilation of King Aemon's army and the Nation of Manetheren perished.
When the details of her treachery became known to the Hall of the Tower, the Sitters voted to strip Tetsuan of her Staff and Stole and condemned her to being stilled. She was kept in the White Tower kitchens and forced to labour as a scullery maid.  Records indicate that she died soon afterwards. In TWoTC it is stated that Tetsuan died three years after her stilling.
Tetsuan is a figure in the history of the White Tower that represents an embarrassment to all Aes Sedai. After more than two thousand years following her death her name continues to be uttered with scorn. She is one of only three Amyrlins to have been deposed and stilled, the other two being Bonwhin Meraighdin in FY 992  and Siuan Sanche in 999 NE. The tragedy of the relationship between Tetsuan and Eldrene is a subject taught to all novices in the White Tower and stands as a grim reminder that no Aes Sedai sister - regardless of position or influence - stands above Tower Law.
Some believe that a more detailed account of Tetsuan's life can be found within sealed White Tower records available only to Amyrlins, Sitters, and a secret group of Brown Ajah tower historians. Aes Sedai sisters will neither confirm nor deny knowledge of such records to outsiders.