A cap table is typically created by a startup's management team and/or board of directors. It outlines the company's current and future equity ownership, and is used to help management make informed decisions about how to allocate equity.
The management team and/or board of directors will work with an accountant or financial advisor to create the cap table. The cap table will typically be updated on a regular basis, as the company raises money, grants equity to employees, or sells equity to investors.