What do you call a person that goes to extreme ends to accomplish a goal?

I've been trying to find a single word that describes a person that will go to extreme ends to achieve a goal.

For example, a person that would harm friends or leave behind a path of destruction to get what they want.

This question about a person that always goes the extra mile was the closest I could find, but didn't answer my question because of its more positive tone.

You have pretty accurately described someone with antisocial personality disorder. Popular terms for this are psychopath and sociopath.

Both types of personality have a pervasive pattern of disregard for the safety and rights of others. Deceit and manipulation are central features to both types of personality. And contrary to popular belief, a psychopath or sociopath is not necessarily violent. http://psychcentral.com/blog/archives/2015/02/12/differences-between-a-psychopath-vs-sociopath/

Ruthless or Relentless

If someone is ruthless to accomplish a goal then that means they will do anything it takes to succeed. The are no boundaries for someone acting ruthless, which can often involve abuse.

A relentless person never stops trying to accomplish the goal, sometimes to the point of being annoying. An example would be a relentless telemarketer calling you everyday.