What technology entrepreneurs have taken the biggest risks in the past ten years?

Has to be the guys at Groupon turning down $6 billion.  Only time will tell if that was the right call.

Steve Jobs. The intel-transition from the PowerPC platform in 2005 was a very bold and risky move because: The PowerPC CPU architecture was one of the key differentiators of Apple from the Wintel world for over 10 years. It could have alienated Apple's few remaining developers (out of frustration) rather than attract scores of new developers into the market. The launch of the iPhone in 2007 was a very bold and risky move because: Apple understood consumers but telecom was not in its DNA or expertise. Phones were long viewed as utilities and not toys. Most of the previous forays into smart phones and devices had been disasters. For both initiatives, Jobs took huge risks but Apple pulled them off and has been rewarded handsomely.

You'll never hear of them because they failed. If what you really meant to ask is "what technology entrepreneurs have taken the biggest risks in the past ten years and succeeded?" then Musk is at the top of the list for going into the automobile industry and the aerospace industry. Both industries are highly developed with powerful incumbents. Some might argue that both industries were ripe for disruption, but it many have tried and failed. The fact that Musk has been successful in both is impressive.