21. Dick Costolo, CEO, Twitter – Most Powerful People in Wireless

21. Dick Costolo, CEO, Twitter – Most Powerful People in WirelessWhat makes him powerful: When Dick Costolo took over the Twitter helm from co-founder Evan Williams in early October 2010, the microblogging platform welcomed roughly 100 million unique worldwide visitors each month. Fast-forward a year later and Twitter now attracts 400 million unique visitors each month, with more than 100 million active users logging in every 30 days. In addition, 55 percent of all active users are active on mobile devices.

And you ain't seen nothin' yet:  Twitter user signups increased 300 percent in the week after Apple (NASDAQ:AAPL) introduced its new iOS 5 mobile operating system, bringing with it deep Twitter integration. 

The Apple partnership represents the capstone of Costolo's first year as Twitter chief, but it's far from the sole highlight. In September, the startup completed the second half of a two-stage investment round totaling $800 million, bringing its valuation to $8 billion. As recently as December 2010, when Twitter received $200 million in funding from Kleiner Perkins Caufield & Byers, its value was $3.7 billion. The funding followed Twitter's latest step towards monetization when it introduced advertiser-sponsored tweets directly into user timelines, promising special offers, exclusive content and announcements from brands, business and charitable organizations that Twitter users already follow. (Estimates suggest that between 20 percent and 40 percent of Twitter users follow a brand or organization.) Twitter is now on pace to generate ad revenues of $150 million in 2011, up from $45 million a year ago, according to research firm eMarketer.

In July, Twitter announced there are now more than a million registered applications across its ecosystem, up from about 150,000 just a year earlier--more than 750,000 developers worldwide produce Twitter apps spanning categories from analytics to curation to publisher tools, and developer activity is so frenzied that a new Twitter app is registered every 1.5 seconds. But Twitter has also ramped up its efforts to institute official branded clients in place of third-party applications, a measure to minimize fragmentation and create a more consistent user experience that nevertheless illustrated that the company can and will throw around its weight as necessary, crushing developers in the process.

But while Twitter has continued to flourish under Costolo's watch, more than five years into its existence the platform remains something of an enigma. What is Twitter, exactly, and where is it going? Costolo contends it is not a social network, so does that mean it's a media company? An ad-sponsored, user-generated news outlet? A recommendations engine? A simple communications tool? Or all that and maybe even more? Twitter seems to be in no hurry to define itself in Wall Street's eyes: Costolo recently said an IPO is nowhere on the company's horizon, adding "We don't need the money. We have more money than we'll need for a long time."

But sooner or later, Twitter will need to establish a clear-cut identity and long-term direction, or else risk squandering the kind of consumer enthusiasm, advertiser attention and investor interest that other startups would kill to amass. It's your move, Costolo. --Jason

21. Dick Costolo, CEO, Twitter – Most Powerful People in Wireless