Dagmar Tan is one of the pre-made child downtownies in The Sims 2: Nightlife. She can be made playable by befriending and aging her up with another child [TS2:FT], and sending her off to college [TS2U]. Dagmar is a C student in public school at the start of the game, and she is mainly interested in Animals and Toys.
Her name is randomized when Downtown is generated. The name "Dagmar Tan" is only referenced in the game files. Like all child downtownies in The Sims 2, Dagmar's facial structure is seemingly exact to one of the default Maxis face templates in Create a Sim. She has the same facial structure as Caryl Zarubin.
Like all pre-made child downtownies, Dagmar has a lifetime want. Her lifetime want is to reach the top of the Athletic career. Note that while this is usually a sign of a problem in a neighborhood, it is normal for a pre-made downtownie child.