Preparing future mathematics teacher educators (MTEs) with knowledge that are needed to effectively support pre-service teachers (PSTs) is very important. However, little attention was paid to MTEs’ knowledge development, which is multifaceted and complex. This study investigates successes, challenges, and tensions that four international graduate MTEs and one mathematics teacher educator (TE) experienced in developing their identity as math teacher educators. In total, 20 h of interactive interviews were analyzed by using qualitative methods. Emerging themes include how MTEs establish a sense of credibility and how they feel they are navigating multiple identities. Among the graduate MTEs, credibility was described as having the following: (a) knowledge of and experience teaching in the US education system; (b) experience in teaching using a problem-solving approach; (c) the ability to enact theory in practice. While navigating multiple identities, graduate MTEs recognize their ethnic identities are central and influence their perceptions of self as MTEs, and how they think they are perceived by others. The results highlight the importance of understanding MTEs tensions and challenges and provide “in-the-moment” support along the journey of becoming teacher educators.