In my experience a senior developer is a lesser-title for a CTO. A senior developer is someone who knows the company's mission, knows the technology, and knows the team. From there they evaluate what the board/CEO/kid with a plan want and develop a strategy to get the not-senior developers to implement that plan.

Key characteristics: Not chasing every new and shiny framework/tech Singular focus on stated objectives/milestones/deliverables Understands "big picture" as well as the granular details, so that they can provide advice and leadership about implementation Acts as buffer between "techies" and management in every cycle of iteration

It's very likely that my bullets are worded poorly, but my overall point is that a senior developer is someone who has the experience to liaison between those with ideas and those with technical skills. In some environments the sr. dev is the person doing the tech work, in other environment they're leading a team, in any case they have the knowledge, skills and experience to produce results.