A question that is up for debate.
A established company has been in the market for a long time. It has a name. It has a proven business model. It has been around.
A startup has been in the market for a short time. It is building its name. It’s business model is not proven yet. It is emerging.
When the company is a startup (new), the founder(s)/CEO is the face of the company. They represent the brand, make it what it is and what it will become. In essence, the founder(s)/CEO make the brand when the company is emerging and not established in the market. On the other hand, when the company is established and already has a recognized name in the market, the brand makes the person. The machine is already built and the person gets their recognition and reputation being associated with it.