The outbreak of COVID-19 witnesses a sudden surge of fully online classes globally. Scholarly attention has promptly shifted to explore the personal experiences and perceived challenges of students and teachers. For English as a Foreign Language (EFL) instructors around the world, many are required to teach online for the first time, yet studies on their teacher identity development in online teaching contexts remain limited. To address this gap, the researchers conducted a case study of three EFL instructors in a Chinese university within an online semester to understand how their online teacher identities developed and shifted. The concepts of 'imagined and practiced identity' and social representation theory have been adopted as the conceptual framework. The findings revealed the trajectories of three online EFL instructors as their imagined identities evolved and renegotiated into their practiced ones based on individual and contextual factors. The findings reveal a lack of rule-based identities from the participants and highlight the need for pedagogical and psychological support for EFL teachers when they transition to an online context. Recommendations are made accordingly.