The field of medicine has made the general public aware of the concept of "patient zero". This is the person who is the first recorded example of a disease that has changed into an outbreak. Outbreaks of diseases like HIV, ebola, cholera, and typhoid have been traced to a patient zero. Finding patient zero is especially important in cases where that person is still alive and spreading the disease their their personal networks.
When I joined a software company a few years ago, I was introduced to the first user of the company's product. I dubbed this person "User Zero" since she was the first recorded example of proof that the software could be a break out success. This was the first person to validate the hypothesis of the value that customers would gain from the software. Without this first confirmation of the company's value proposition, the company may have never existed.
Most companies focus on gaining new customers and neglect their User Zero. I believe this is a mistake. Your User Zero has experiences and memories of your application that few people can match. Your User Zero can hold you accountable to the ideals and principles upon which your company was founded. This accountability is vital because those ideals and principles are easy to lose in the race to close the next sale. Furthermore, your User Zero is often the biggest champion of your product. You should regularly meet with your User Zero and keep her abreast of the features you plan to add to your product. Your User Zero can then become an even greater advocate for your company, especially if she has a large social media following. Just as patient zero is key to understanding the spread of disease, your User Zero can be a vital part of understanding the infectious power of your software.
Ideally, you will bring your User Zero into your company as an employee and have them actively involved in developing your product. I have seen several companies turn their User Zero into a very effective Product Manager (or Product Owner for Scrum teams). By drawing on her domain expertise, industry knowledge, and history with your company, your User Zero can help you find features that have a high value to your existing customers. By integrating your User Zero tightly with your Development Team, you can mine these features to find the ones that can be delivered at the lowest cost. Delivering high value and low cost features to users is one of the best ways to delight both your customers as well as the internal business functions of your company. The key to unlocking this dual-delight effect is your User Zero.