Teachers of all school subjects have an important role to play in developing the numeracy capabilities of students. However, to fully exploit the numeracy learning opportunities that exist in the subjects they teach, teachers need to have an identity as a teacher of numeracy. In this paper some findings are presented from a two-year study designed to investigate how teachers develop this type of identity. The specific purpose of this paper is to present a preliminary case study of one of the teachers to illustrate how an adaptation of Valsiner's zone theory can be employed to describe and analyse a teacher's identity as an embedder-of-numeracy. Drawing on interviews and lesson observations, a preliminary case study of a secondary school history teacher is presented. The case study includes information about the teacher, his professional context, and a classroom vignette to illustrate practice. Data are mapped onto the teacher's Zone of Proximal Development, Zone of Free Movement, and Zone of Promoted Action and his identity as an embedder-of-numeracy is described and analysed in these terms. The analysis suggests that there are several ways that this teacher could be supported to develop his capacity to embed numeracy into the history curriculum.