TLDR:
A co-founder is a person who joins others in creating a company, typically participating in the founding vision, strategy, and equity ownership during the formation phase.
Co-Founder Structures
Co-founder arrangements should be formalized through founders’ agreements covering equity splits, vesting schedules (typically 4 years with 1-year cliff), roles and responsibilities, decision-making authority, IP assignment, and what happens if a co-founder leaves. Best practice is to address these issues early — disputes between co-founders are among the most common causes of startup failure.
Equity Considerations
Equal equity splits are common but not always optimal. Considerations include who originated the idea, time commitment, prior work invested, capital contributed, and respective skills. Many successful companies have unequal splits reflecting these differences. Whatever the structure, all founders should be on vesting schedules to protect the company if someone leaves early.
Selecting Co-Founders
The right co-founders bring complementary skills, shared vision, mutual trust, and ability to handle stress and conflict. Common combinations include technical + business, product + sales, and domain expert + operator. Founders should have honest conversations about working styles, risk tolerance, family situations, and long-term goals before committing — these conversations are far easier before starting than after disputes arise.