He is confronted in his subzero lab by Roy and Leon, the latter of whom rips open Chew's thermal coat to make it easier for Roy to interrogate him.
What does it mean by this highlighted sentence?
"the latter of whom" is a relative construction that refers back to the second-mentioned of the two people, "Leon". You can think of "the latter of whom" as a proxy for the noun "Leon". We use "whom" because people are involved. The same construction can be used with things, in which case we use "which" instead of "whom".
The medicine cabinet contained a bottle of aspirin and some ipecac, the latter of which induces vomiting.