Final answer:
To know who the first person to get the 'Postmortal' achievement on a server was, one would need access to that server's records or information from the game's community managers.
Step-by-step explanation:
The question you've asked pertains to a specific achievement, 'Postmortal', on a server, likely within a video game or similar digital platform. Determining who was the first person to obtain a particular achievement on a server would require access to the server's records or announcements made by the server administrators or the community managing the server. Since this type of information is usually specific to a particular game or platform and not universally documented, it would be difficult to provide an accurate answer without additional context or access to the server's history and data.