Which tool in Power BI is designed for creating complex data models?

The Power Query Editor is specifically designed to facilitate the process of transforming and shaping data. It allows users to perform various data preparation tasks, such as filtering, merging, and aggregating datasets before they are loaded into the Power BI data model. This tool is crucial for creating complex data models because it enables users to cleanse and structure their data in a way that enhances the model's overall effectiveness and efficiency.

By utilizing the Power Query Editor, users can manipulate and combine data from various sources, ensuring that the datasets are tailored for analysis. This can involve intricate operations such as establishing relationships between tables and creating calculated columns, which are essential elements of complex data modeling.

While the DAX Function Editor is important for creating measures and calculated columns within the data model, it doesn't directly aid in connecting or shaping the raw data. The Data Visualization Designer focuses on creating reports and dashboards from existing models, and the Report Builder serves a different purpose by allowing users to create paginated reports. Therefore, the Power Query Editor stands out as the primary tool used for crafting complex data models in Power BI.