Chinese billionaire Pony Ma does not flaunt his strategies like Alibaba's Jack Ma or Japanese mogul Masayoshi Son.

Pony Ma's company, Tencent, has moved with the stealth of its founder this year, making a series of investments in Western companies that are significant, but not splashy: A 5 percent stake in Tesla, a 10 percent stake in Snap, an investment in Essential Products, and now, reportedly, a 10 percent stock swap with Spotify.

With the possible exception of social media company Snap, these companies — a carmaker, a phone maker and a music streaming app — have little to do with WeChat and video games, all part of Tencent's core businesses.

Yet they do have something in common: They are among the few companies that are considered contenders against companies like Facebook, Apple, Amazon and Google.

Tencent may not be well-known to American consumers, but it recently became the first Asian tech company to be valued over $500 billion, on the heels of companies like Facebook and Amazon. And its long enjoyed a 'frenemy' sort of relationship with the biggest U.S. Internet firms.

Amazon helped back Tencent's investment in Essential's new phone, for example, and Tencent-backed "League of Legends" is a popular attraction on Amazon's gaming platform, Twitch. At the same time, Tencent launched a U.S.-rival to Amazon Web Services.

Analysts have pointed to WeChat's popularity in China as a major challenge for Apple — which in response has tried to beef up its own messaging platforms and offer prompt cooperation with Chinese lawmakers. (When asked about this relationship recently, Apple CEO Tim Cook said, "I see Tencent as one of our biggest and best developers," and pledged to work more with Tencent going forward.)

Facebook's relationship with Tencent is perhaps the most rivalrous. According to a report in Bloomberg Businessweek, Facebook CEO Mark Zuckerberg swooped in on Tencent's talks to acquire WhatsApp while Ma was recovering from back surgery.

And in addition to its stake in Tesla, Tencent has also an autonomous car project, a health diagnostics platform, advertising services, and other "moonshot" projects that should sound familiar to any investor in companies like Alphabet.

As 2017 comes to a close, it's more clear than ever that Tencent is a silent threat to American technology giants. The company lurks under the guise of mid-sized companies across Silicon Valley, ready to ambush.

When critics have questioned whether upstarts like Snap or Spotify can take on Facebook and Apple, Tencent has come to their defense behind the front lines and strengthened their odds.

Perhaps the enemies of Tencent's enemies can look forward to more big checks.

Disclosure: CNBC parent NBCUniversal is an investor in Snap.