Customs Agent
According to O*NET Online, the main role of a Customs Agent (aka Customs Inspector) is to investigate and inspect persons, goods, common carriers, and merchandise, arriving in or departing from the United States or between states to detect violations of immigration and customs laws and regulations.
Customs Agents work for the United States Department of Customs and Border Patrol, which is a branch of the DHS (Department of Homeland Security). A custom agent that works for the CBP is responsible for helping keep weapons and terrorists out of the United States. They are also responsible for preventing smuggling and illegal immigration.
There are some customs agents that have an extensive knowledge of immigration laws and specialize in working with immigrants. Other agents are trained in how to handle guns and narcotics and work exclusively in that department. Customs agents work all over the country at land border crossings and in airports. These individuals are the first line of defense against a number of risks to national security.