The cell kingdom that includes both multicellular and unicellular organisms is the Protista kingdom.

Here's why:

* Protists are a diverse group of eukaryotic organisms.

* Unicellular protists are common examples like amoebas, paramecia, and algae.

* Multicellular protists are less common but exist, such as some types of seaweed.

While other kingdoms like Fungi, Plantae, and Animalia are primarily multicellular, the Protista kingdom uniquely encompasses both cellular structures.