In StarCraft II, the Zerg unit that can create Creep Tumors and spread creep is the Queen.
Creep is the purple biological terrain produced by Zerg structures and certain abilities. Zerg units move faster on it, while most non-Zerg units cannot normally build or operate there in the same way. Queens extend this territory by using their Creep Tumor ability.
A Creep Tumor is a hidden biological structure that spreads creep and can create additional tumors, allowing creep coverage to expand across the map. Tumors are immobile and vulnerable if detected, so players often place them along likely attack routes and near expansions.
Queens have several other important responsibilities, including injecting Larvae into Hatcheries, attacking air units, and defending bases. Their ability to spread creep therefore connects scouting, mobility, economy, and defense rather than serving as a purely cosmetic feature.