Answer and Explanation:
Meyer Wolfsheim is a character that does not appear much in "The Great Gatsby". Still, it is enough for us to infer a few things about him. Let's keep in mind that the story is narrated from Nick's perspective, which means it is a biased narrative.
Wolfsheim meets with Nick and Gatsby at an underground and illegal bar (the story is set at a time when alcohol was prohibited). He is constantly looking around, as if he is searching for possible threats or enemies. Nick notices he wears human molars for cuff links. That is a sign that Wolfsheim is most likely a dangerous man. It is also revealed that he is not only a gambler, but a powerful one - influential enough to fix the 1919 World's series.
Therefore, we can safely say Wolfsheim is a criminal. He seems to be a bit paranoid, and he is certainly a dangerous man. As for his contribution to the novel's conflicts, the most important seems to be his connection to Gatsby. They are clearly "business" partners. Wolfsheim is the man who helped Gatsby become wealthy by selling illegal alcohol.