Founder

Someone who was there when the business or product was created and contributed to it . It doesn’t necessarily mean that the person has control over business or has equity . It is only a namesake and is not much associated with any managerial responsibilities

Partner

Could be from the beginning of the product/company/service , or could’ve just joined in between . Partnerships are temporary and invovles active participation in running of the business and has some control over profit /losses.