Elon Musk has called artificial intelligence mankind's "biggest existential threat."

At its simplest form, think of AI as personal assistants like Apple's (AAPL) Siri or Alphabet's (GOOGL) Google Now.

The AI industry offers tantalizing growth, with BofA saying the market for AI-based analytics is likely to grow tenfold to $70 billion by the end of 2020.

The sophisticated technology is being combined with machine learning and voice recognition to tackle major challenges and threaten previously-untouchable jobs of knowledge workers like customer-service representatives.

Google is a clear leader, with dozens of AI patents and the acquisition of neural network developer Deep Mind.

IBM (IBM) is also a pioneer in AI. The company's IBM Watson supercomputer can read a million medical textbooks in just three seconds and has even defeated the greatest Jeopardy champions.