This study investigates the characteristics of an L2 expert teacher educator. The expert participant was selected based on the criteria suggested by educational expertise studies: years of teaching experience, high reputation among multiple constituencies, and evidence of impact on student performance. The data collection included observations, interviews, and artifacts. The observations took place in a Master's course at an American university in Asia. I conducted interviews with the focal participant, his three students, and a colleague. The evidence reveals a developmental process of expertise that includes reflecting, reading, writing, and sharing through teaching and publishing. One of the synthesized products of this process, his framework for curriculum design, is described in relation to his expertise. His practice is characterized by his manner in reasoning, engaging tasks, and supporting other researchers thereby contributing to the academic community.