The nucleus controls all the activities of the cell. It is the headquarter of the cell.
The lysosome has various functions, including killing pathogens. It also plays a role in cell death, and hence is called a suicidal bag.
Mitochondria are involved in extracting energy from food and storing it in the form of ATP. Therefore, they are called the powerhouses of the cell.
The Golgi apparatus is involved in packaging and transportation. So, it is called the post office of the cell.