"human-smuggler" or "snake head"?

"Human smuggler" or "human trafficker" (the latter is used more often I think) would be a more formal way of describing the person. "Snake-head" is slang I think but I don't know its origin.

Both terms refer to smuggling illegal aliens across a border.

"Snake head" is much more colorful than "human smuggler" although snakes are not necessarily highly regarded.

I've also read of "coyote" being used as a term for the guide to illegal aliens. Here the play on words is "one who can survive in harsh circumstances", but the coyote doesn't much care whether his flock survives.