This isn't the first COO the company has ever had. That role was previously held by George Hu, the guy that famously started at Salesforce as an intern and worked his way up to the No. 2 slot over 13 years.
Hu left Salesforce the end of 2014 to found his own startup, Peer, (with the blessing, and financial backing, of Salesforce CEO Marc Benioff, who is a huge angel investor).
Meanwhile, Block has done extremely well at Salesforce since he left his old alma mater, Oracle, about a year before joining Salesforce. Block had been head of North American sales.
He left Oracle after a controversial bunch of instant messages and e-mails from him surfaced during a lawsuit between Oracle and HP, some of them saying less-than-nice things about Mark Hurd's strategy. Hurd was a president for Oracle at the time in charge of sales (and has since been promoted to a joint CEO role, a job he shares with Safra Catz).
In 2014, Benioff called Hurd's decision to dismiss Block "the biggest mistake Mark Hurd ever made." (Sources close to Oracle told Business Insider at the time, that decision to let Block go wasn't entirely Hurd's alone.)
Salesforce and Oracle are fierce rivals since Oracle has turned its attention towards cloud computing, where Oracle is a relative latecomer. Oracle's executive chairman Larry Ellison frequently names Salesforce as one of his biggest competitors.
Meanwhile, Block found his calling running sales at Salesforce. In the time he's been there, Salesforce's revenues and bookings have skyrocketed.
The company has promised revenues will hit over $6.6 billion for its current fiscal year when it announces those results probably later this month. And it's on track to hit $8 billion next year, it says, up from $3.05 billion in 2013 the year Block joined. Benioff says the company is quickly marching toward $10 billion, too, and names Block a key player in its success.