Here he is, folks. Medieval knights don't get much better than this.
As a knight, Tristan is everything you could want. He's been trained by the best, and he can do it all. His dad made this all possible by entrusting Tristan's education to that wise man Governal, who taught him "all the warlike and peaceful arts" (1.39). What are those, you ask? Awesome things like swordplay, jousting, hunting, music, and languages. So he's got all these amazing skills, and on top of that, he's an all-around good guy.
Tristan shows his amazing knightliness when he first arrives at King Mark's court. Tristan's mad skills and accomplishments set him apart from Mark's other knights right away, making him a favorite of the king even before he learns that Tristan is his nephew. In Ireland, Tristan's expert harping attracts the attention of the Irish king whose daughter, Yseut, manages to heal his poisoned wound. And oh yeah, did we mention that he received that wound by beating a scary Irishman in a fight? (Cough Yseut's uncle cough.) When it comes to his knightly skills, Tristan is the best of the best. It's hard to believe that Yseut needs a love potion to fall for this hunk. After all, here's a guy who can kill dragons and play the harp.
Now, Tristan may be a real quarterback of a knight, but what's even more important in this society is his relationship with his lord, to whom he owes loyalty, respect, love, and even his life. At first, Tristan is a great vassal: He's such a loyal vassal to his lord, King Mark, that the two have a real medieval bromace going on. (At least at first.) Tristan's the only one willing to fight Morholt, for one thing. He's also the only one who steps up to help find the woman Mark declares he wants to marry.
Of course, that's where all the problems start. Thanks to a powerful love potion, Tristan falls in love with his lord's future wife as he's escorting her to marry him. Yeah, that's so totally crossing the line for any good vassal ever. And it's not like Tristan decides to love Yseut from afar; instead, she and he continue to meet secretly, sometimes in the king's own bed, even after Mark's suspicions get Tristan thrown out of the palace. Unlike Meatloaf, Tristan will do anything for love—and he will do that.
Despite this ultimate betrayal of his lord (oh, yeah, and also his adultery, which medieval people didn't like so much), this story isn't all that interested in making us think badly of Tristan's actions. As Yseut explains to the pious hermit Ogrin, she and Tristan can't help loving one another "only because of a draught that I drank and he drank" (7.79), a plot point that serves to lessen their guilt. Instead of the lovers looking traitorous, it's Mark's barons that get a bad rap for their "lies," and Mark who appears stupid and disloyal for believing them.
It's also possible that Tristan is destined for unhappy or unlucky love, since, after all, his mom died giving birth to him, and he got the name "Tristan"–basically, "sad dude"–because of it. So even from birth, love (he's the product of his parents' love, after all) and death are intertwined for him. It's another way in which Tristan seems to be fated to do what he does in the story. It's also possible that it's Tristan's very capacity for deep, tragic love that separates him from the other knights and makes him so awesome. Now there's a thought. There are all these hot dudes everywhere in medieval literature, but it's the one with feelings who turns out to be the most interesting.
Now, Tristan seems pretty perfect, but like Yseut, he does do a few things that even the love potion can't excuse. When he marries White Hands, it's not as if he's really thinking about her best interests, right? For that matter, what's up with getting healed by the niece of the Irishman you just killed, then winning her in marriage and turning her over to the guy who wanted that Irishman dead in the first place? And why is Tristan helping Kaherdin get it on with some other dude's wife? Tristan is definitely our hero, and we want to take his side, but it's complicated, you know?
Anyway, instead of condemning Tristan, we're encouraged to admire him. He's a lover, he's a fighter, and he's also pretty clever (though Yseut probably gets the gold star for cleverness in this story). Tristan comes up with all kinds of ingenious ruses to avoid capture. His elaborate performance of innocence and loyalty when he knows Mark is eavesdropping; spectacular escape from his captors and leap from a cliffside chapel to the seashore below; and successfully executed disguises as a leper and a clown mark Tristan's cleverness and skill. Never mind that these are all means by which he tricks his lord and continues to sleep with his wife: the point here is that Tristan is awesome. Love is the ultimate good in this story, and Tristan its most loyal knight.