Tartrate is a legendary player on KGS, who is known for his fabled invincibility, which has only been broken twice, the first time against Charm, the second time against Gentlerain. In both of these games he took White with no komi, and lost on time. Opponents left in his wake include Alexandre Dinerchtein 1p, Svetlana Shikshina 1p  and mymy (6p at the time). The ease with which he dismissed the plethora of opponents, makes many people believe Tartrate is a strong professional. While amicable and somewhat chatty, he has chosen to remain anonymous, and will not answer personal questions such as where he comes from or whether he is a pro. Don't bother asking him about his identity.
His overwhelming appearance in 2003 was followed by a long silence, which ended when he made a short comeback in January 2004, continuing his winning streak as expected. His game against Weems 9d attracted over 400 observers. But by the end of the month, tartrate vanished from KGS. After 6 months, his account was deleted due to inactivity and over the next four years the account was registered many times by several fans and trolls.
In 2007, a player by the name of tartaric appeared on KGS and rapidly reached the rank of 9d. Though his record contained a few losses, his name and performances led many to believe that Tartrate had returned. This theory was dispelled when it was revealed that Tartaric is actually Peter Liu (Liu Yuanbo) 2p from China. He's one of the main teachers in the Go to China trip and made the account during the last trip to draw spectators and speculation.
In March of 2008, reliable sources announced that the real tartrate would come back to KGS to play Gentlerain in an even unranked game. Indeed he did return, and although he lost, his match was very exciting and attracted over 800 spectators who clamored to see the return of the Legend. Details about this game can be found at Tartrate vs Gentlerain. After being absent for four months, tartrate returned to KGS on the 4th of July, and as so far played two games, winning both. It is unknown if tartrate will continue to play regularly on KGS, or if he will vanish from the internet again like he did four years ago.
Tartrate has a message for the online Go world: he STRONGLY suggest that while he is playing games, all the dans (especially higher dans) comment on his game for the community, and is angry and disappointed when they don't.
In the spirit of good fun, what is your tartrate number?
There is currently much speculation that the tartrate that played gentlerain (losing by time) was not the tartrate from 2003. Evidence in favor is playing style and personality.
 It is unknown whether tartrate is male or female.
 On January 16th, 2004, tartrate lost against charm. However, this was a no komi game with tartrate taking white. The game was lost on time, and, while tartrate may claim (s)he was losing at the time, it is generally acknowledged that (s)he would have won.
Charm is actually another account of the KGS Teacher "sendol". Sendol seems to have a go school in Seoul, Korea and has recently started teaching on KGS.
Before that, Tartrate did lose a few games on May 22, 2003. Of course, they were part of an 11-game simul, the majority of which he/she won. However, that impromptu simultaneous test suffered from a serious miscalculation of the time needed to deal with so many games, and casts no reflection on the ability of tartrate to play Go most excellently.
The game was lost by time, however, with white leading by about 10 points. Please comment if my counting went completely astray. In other words, with nothing astounding happening in the end-game any longer, it would have been a victory for Tartrate without doubt. --Sigmundur
Perhaps you counted more closely than tartrate himself, because he seemed to say that he was actually losing at the time. --''Lynx''
 The match between tartrate and Shikshina ("redrose") was an impressive fighting game, with tartrate opening at Tengen. The game involved two large semeais and two large ko fights and ended to a resignation by Shikshina. The game record can be found with the usual KGS kibitz at http://files.gokgs.com/games/2003/6/18/redrose-tartrate.sgf.
 Hylebos: Actually that was the real Tartrate. Though his identity is a mystery to most, he had several close friends who he shared his identity with. Those friends confirmed that he was the real tartrate.