Character Analysis
Sook Yongsheng is a local hatter—which, as Anna helpfully explains at one point, is a digger who digs alone. He gets a lot more attention among the characters and in the plot for his role as the proprietor of an opium den that was previously a favorite destination of Anna Wetherell. According to our omniscient narrator, some of Sook's defining characteristics are that he feels "universally misunderstood" (I.11.239) and had a "sense of being constantly undervalued by the world" (I.11.239). Poor guy.
Based on what we see of Sook's social life, those observations are pretty much on point—people often don't understand/respect Sook (or even try), in large part because of racism and the language barrier between him and the English-speaking residents of Hokitika.
He's also not very well known because he's kind of a loner:
It was by preference, and not by necessity, that Sook Yongsheng lived and worked alone. He was not surly by temperament, and in fact did not find it difficult to form friendships, nor to allow those friendships to deepen, once they had been formed; he simply preferred to answer to himself. He disliked all burdens of responsibility, most especially when those responsibilities were expected, or enforced—and friendship, in his experience, nearly always devolved into matters of debt, guilt, and expectation. Those men he did choose to call his intimates were those who demanded nothing, and gave as much; as a consequence, there were many charitable figures in Ah Sook's past, and very few upon whom he had expressly doted. (I.11.239)
In short, Sook is kind of isolated from his fellow man by both circumstance and his own disposition.
What's Your Sign?
Sook is associated with the sign of Aquarius. Aquarians are known for having a strong social consciousness and wanting to make life better for others. Sook fits in with that description well enough, since he certainly thinks that killing Frank Carver will make the world better. Like the 11 other characters assigned to zodiac signs, he was among the men who met at the Crown the night the book opens.
The Demon Carver of Kaniere
Sook actually ends up playing a pretty big role in the story, but unfortunately his ride is pretty tragic…and ends sadly. And of course, the sad stuff all traces back to Frank Carver (as is more or less much the case with everyone's problems in the story).
Sook met Carver when he was a little boy and Carver was in his early 20s. Carver did business with Sook's family and, unbeknownst to the Sooks, started using their business as a cover for his opium running. Yeah, not cool. As a result, Sook's father ended up being executed when their warehouse was raided. Even more not cool.
When Sook figured out that Carver was behind his family's downfall, he swore to get revenge on his old buddy, following him to and around New Zealand to try to bring that plan off. But it wasn't meant to be—and George Shepard, who unjustly blamed Sook for the death of his brother, killed him just as he was about to avenge his family at last.
However, Te Rau Tauwhare ends up doing the job for him when he kills Carver to avenge Crosbie's death. We guess that's the convenient thing about going against a super villain—if you can't get the job done, chances are there's someone else around ready to step in and finish him off.
Sook's Timeline