Deliver industry-changing projects with proven results and know your industry/domain; this could also be projects that open up new markets for the org. While I think senior developer is achievable without domain knowledge of the industry, I fail to think of a single principal or fellow I've met who did not have deep understanding of the field they're in. Some had patents to their name, some didn't; all had 'proven' in some way that they're indispensable for their respective domain.