The major chemical energy currency in life in eukaryotic cells is ATP (Adenosine Triphosphate). The major contribution of ATP in eukaryotic cells comes from mitochondria. Every cell in your body contain mitochondria. Mitochondria then might be called the most successful organism on the planet since they:

First of all mitochondria is not an organism it is an organelle in most cells.

Biochemical processes like respiration and energy production occurs in mitochondria and therefore it is also known power house of the cell.

Explanation:

As it is a source of energy production therefore it is called as powerhouse of cell.