The Nucleus is the control center of a cell. It protects the DNA and makes sure the DNA is available for use at the proper times. When DNA is needed, it produces copies of itself in the form of RNA. The nucleus also contains the nucleolus which is a region of the nucleus made up of ribosomes which are a combination of proteins and RNA.
The Nucleus is the town hall of Cell City because it's the control center. Town halls help control the town and give out copies of the rules and laws, similar to how DNA and RNA work in a cell.