Walter's living the life... at least that's what he thinks, and that's the way he wants it to stay. Marriage? That's for chumps who want to lose their freedom. This dude would rather hunt and hawk all day.
Walter is young, carefree, and living in the moment. Don't fence him in.
But wait, isn't he also the lord of, like, all of Salucia? Doesn't he already have a boatload of responsibilities? He doesn't think being marquis of Salucia limits his freedom? Something's up with this guy: either he's totally naive about the responsibilities that come with being a leader, or he's simply thoughtless about the future... or both.
The Clerk, for one, isn't too impressed by Walter's thoughtlessness: "I blame hym thus, that he considereth noght / In tyme comynge what hym myghte bityde, / But in his lust present was al his thoght" (78-80). In other words, all Walter does is think about himself and his own desires. Maybe he's never really had to think about anyone else; unlike Grisilde, he's grown up rich and powerful. People have probably respected and feared him all his life just due to his status.
When Walter's nobles ask him to marry, they're also asking him to step up to the plate and take on the responsibilities of a leader... and those responsibilities include thinking about other people's needs and desires. As we discuss in our "Themes" section, Walter's people are loyal to Walter's bloodline—not just to Walter himself—so by refusing to marry (and thereby continue the bloodline), Walter is shirking his responsibilities as ruler. He thinks everything is about him, but he fails to see his role in the big picture.
So, what happens when Walter decides to actually marry? Does he see the light and start thinking about other people's needs and desires? Well, the first thing he does is ask his wife-to-be to promise that she'll give up her own desires and submit to him completely, at all times. Not too promising, is it? Even after his marriage, he is unable to resist "this merveillous desir his wyf t'assaye" (454). That's when Grisilde's trials begin, and they're dictated by nothing more than the whims of a husband unable to control them and accustomed to getting his way.
Now, some people think that Walter is meant to serve as a God-figure in the tale, and at one point the Clerk himself claims that Walter and Grisilde's relationship is meant to demonstrate the proper one between God and the Christian soul. On the other hand, the intensity with which the Clerk hates Walter's behavior—not to mention the behavior in and of itself—makes him seem like just a tyrannical husband... well, one with much more power and a more willing victim than such husbands are likely to have, anyway.
Walter's not an entirely negative character, though. The Clerk tells us he is "a fair persone, and strong, and yong of age, / And ful of honour and of curteisye, / Discreet ynogh his contree for to gye" (73-75). The fact that his nobles and people are readily obedient to him suggests that as a ruler he is fair and just, able to command loyalty from his followers. The Clerk constantly reminds us of Walter's great nobility of descent—"To speke as of lynage" Walter is "the gentilleste yborn of Lumbardye" (71-72).
Of course, Walter's nobility in and of itself doesn't make him a good person. He himself says, as he's thinking about getting married, that "bountee comth al of God, nat of the streen, / Of which [children] been engendred and ybore" (157-158). In this tale, Walter's "bountee" or goodness gets put to the test as much as Grisilde's does. Does Walter's status as a competent ruler make the way he abuses power in his marriage better? And how does his "bountee" measure up next to that of someone "povreliche yfostred up," like Grisilde? (213).
Walter does do some pretty questionable things throughout the tale, but it's possible that this is at least partly the story of Walter learning to get past his narrow focus on his own desires. He stops tormenting Grisilde, after all, because for once, he seems to be truly moved by the feelings and desires of someone else. Maybe it's only at the very end of the tale that Walter learns what it means to be truly "noble."