Jeroen ter Heerdt is a principal product manager on the Power BI team at Microsoft and one of the masterminds behind visual calculations. With a focus on advancing DAX and modeling in Power BI, Jeroen is passionate about delivering powerful features and improvements that empower users. Known as the “Dutch Data Dude,” he is a seasoned speaker and advocate for data-driven insights, captivating audiences with his entertaining and thought-provoking presentations. Known for incorporating unique and delightfully “weird” elements into his keynotes, Jeroen leaves a memorable impression every time he takes the stage. You can find him sharing insights and connecting with the community on social media as @jaypowerbi, on Reddit as @dutchdatadude, on LinkedIn, and through his website, https://www.dutchdatadude.com. He frequently reminds himself to return to blogging more regularly. When not immersed in the world of data, Jeroen enjoys experimenting with artisanal food and drinks, home automation, and exploring the beauty of the Pacific Northwest.Madzy Stikkelorum has a master’s degree in Mathematics, and analyzing data has always been one of her passions. She currently works as a data analytics consultant at Quanto, where she enjoys helping clients solve complex problems with Microsoft Power BI solutions. She shares her love for Power BI and DAX with the community by organizing the Power BI Summer School in the Netherlands, as a public speaker at international conferences, and in blog posts, which can be found at https://quanto.eu/blog/. Her very first video training about DAX, created with Michiel Rozema, launched in 2025 for Microsoft Press. Madzy is married to Wouter, and they already had one son together, but during the writing of this book, their second son was baking in the oven—inspiring Madzy to ensure she met the deadlines for her chapters! In her spare time, she loves to read, bake, and work on creative projects of all kinds. This is her first ever book as a co-author; she is extremely proud to have a book of her own making in her bookcase and is sure that more will follow.Marc Lelijveld is a Microsoft Data Platform Most Valuable Professional (MVP), solution architect, and technical evangelist with a passion for turning data into action. He focuses on Power BI and Microsoft Fabric, helping others make the most of these technologies through practical insights and real-world experience. Recognized as a Microsoft MVP since 2018, Marc is a regular speaker at international conferences, user groups, and community events. He’s known for sharing his knowledge, best practices, and contagious enthusiasm—whether he’s presenting deep technical content or inspiring others to level up their data journey. Marc blogs about Power BI and Microsoft Fabric at https://datamarc.com and can be found on most social platforms under his own name. When he’s not working with data, you’ll probably find him out exploring the world on one of his many bikes.
