Endomorphism Ring of Abelian Group is Ring with Unity

Theorem
Let $\struct {G, +}$ be an abelian group.

Let $\struct {\map {\mathrm {End} } G, +, \circ}$ be its endomorphism ring.

Then $\struct {\map {\mathrm {End} } G, +, \circ}$ is a ring with unity $I_G$, where $I_G$ is the identity mapping on $G$.