Besides the improbable achievement of becoming the most recognizable entrepreneurs in Japan, Son, known by the nickname “Masa,” has proven to be an extraordinary investor. He wagered early on Yahoo Japan and Alibaba. The latter investment alone may be one of the greatest investments ever, parlaying a bet of about $200 million into a stake worth in the neighborhood of $70 billion.

Arora says Son aims to turn his “hobby” of investing into a foundation for the future of SoftBank. Already, Arora has had a busy nine months. Since he joined the company SoftBank has made nine investments, including the recently announced $100-million stake the U.S. geolocation advertising technology company Banjo. Others include a $250-million stake in GrabTaxi, an Uber competitor in Southeast Asia; a $627-million investment in Snapdeal.com, an Indian e-commerce company; and the $90 million SoftBank invested in housing.com, a property site in India.

SoftBank also was rumored to have attempted to acquire the ailing film studio DreamWorks Animation, a deal that was said to collapse just before it was done.

Son surprised the technology and investing world earlier this week by announcing that Arora would become SoftBank’s president in June, making the Indian-born executive part of a top-level management team that includes Ron Fisher, a 20-year SoftBank veteran. Son, 57, also anointed Arora, 47, his likely successor as CEO, though he has no plans to retire.

Arora, who was in Japan for the announcement, returned mid-week to Silicon Valley, where he is based. He answered questions about his role at SoftBank, the nature of his relationship with Son, and the future for SoftBank’s risky acquisition of the laggard U.S. telecommunications company Sprint.

How did you come together with Masayoshi Son?

Masa has been spectacularly successful over the last 37 years in identifying trends, investing in them–either by putting money into them or investing in the entrepreneurs behind them—through joint ventures, or by doing it himself. He bought Vodafone Japan and made it into SoftBank. He identified the importance of the iPhone and, by working with Steve Jobs, he got exclusivity in Japan. Very few No. 2 or No. 3 networks have been transformed into successful companies. He saw the opportunity.

He’s also a great investor. He turned a less-than-$10-million investment in Yahoo Japan into a 40% stake worth around $8 billion to $10 billion. Alibaba is not his first big return. He’s been very astute in his ability to identify trends. If you look at the evolution of Softbank it’s been a strong Japanese business with one person as a global CEO and with Masa doing all the investing. We met six years ago when Yahoo and Microsoft were doing their search deal. They hadn’t spent a lot of time figuring out Yahoo Japan. He wanted to make sure they had the best search, and he came to Google and sat down with me. He structured a deal that didn’t conflict with Yahoo. It was another instance of him anticipating a trend. And when he does a deal he acts boldly, without nickel and diming anything. That’s when we became friends. He is always true to his word and focused on the big picture.

We spent a lot of time talking about the telecom market. We ended up going from peripheral conversations to deep conversations to Masa saying, ‘Why don’t we work together?’ He said, ‘I need to take what I do as a hobby, investing in global technology companies, to investing being part of SoftBank’s future.’

How are you approaching the task of investing on behalf of SoftBank?

For me it’s almost like a very well-funded startup playing in the big leagues. It has a strong balance sheet, and more than 50% of the assets are outside of Japan. We started talking about everything. He, Ron Fisher and I all spend time with Marcelo [Claure, the CEO of Sprint]. We also spend time on the Japanese business. I’ve spent a lot of time with the entrepreneurs of the Indian companies we’ve invested in. So I’ve spent the nine months investing, working with portfolio businesses, and starting to build a global team.

What types of investments are you looking for?

Masa and I share an insight: If you look at innovative companies, almost every one goes through a lifecycle. It creates disruption, becomes a market leader, and then matures, either because the founders move on or the business model is copied and competition increases. Then it becomes very hard to be the innovation leader. We sat down and said: How do you create innovative companies for the long term? One way is to find the entrepreneurs and nurture them. If we can find five to ten people to work with every few years we’ll build for the future.

What themes should we take away from the companies SoftBank has invested in recently?

We’ve been more opportunistic than thematic. The theme is that we want to make sure it’s a big addressable market. Masa has a saying, that of two small fish, one will become a whale and the other will become a tuna. We obviously want to invest in the fish that will become whales.

Would you like to comment on Verizon’s agreement to buy AOL?

No. There are so many related situations with Sprint, a competitor to Verizon, and Tim [Armstrong], who I worked with at Google.

Did SoftBank ever comment about its attempt to buy DreamWorks, and would you like to now?

No.

What are your thoughts on Sprint?

After Masa acquired the assets, we should have gone for restructuring faster. Now Marcelo is cleaning up the things that should have been cleaned up a while ago.

I interviewed Arora five years ago at Fortune Brainstorm Tech in Aspen. Our conversation was a spirited review of where Google stood at the time. The full video can be seen here.

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