An engineer who joined Twitter in early 2007 and later earned the title "API Lead" has now left the company.  Alex Payne announced this afternoon that he’s quit, and will be moving on to act as cofounder, CPO, and CTO at a startup called BankSimple.

This is obviously bad news for Twitter in the sense that Payne was a valuable employee.  Twitter’s developer platform has played a huge role in making the site popular, and Payne’s experience would have been an asset as Twitter continues to grow.

The situation could be worse, though.  One important thing to note is that Payne hasn’t left Twitter for a competitor (or a company looking to become a competitor).  BankSimple is just supposed to be, as its name implies, a customer-friendly bank.

Also, in a blog post Payne linked to in a tweet, he explained, "Walking away from Twitter wasn’t an easy decision.  Working there has been a life- and career-changing experience.  I’ve learned all sorts of lessons, made great friends, and worked on something that millions of people now use every day."

A more interesting story might develop if and when Twitter names a replacement, then.  We know Payne was good, but Twitter’s future may start to look worse or better depending on who it promotes or hires to take over his duties.