The answer is carbon.
The reason this element gives so much diversity is due to its valency of +4. This means it can bond with many elements in different ways to form different compounds. Carbon can also bond with other carbon atoms in many different ways (from linear chains, branched chains to rings). It is due to this versatility that carbon is the central elements of organic life. The different organic molecules that carbon is the central atom is DNA, carbohydrates, proteins, lipids, and etcetera.