Researchers and educators have always strived for creating appropriate instructional tools and resources that help students to acquire knowledge. Animated pedagogical agents (APAs) embedded within multimedia learning settings are one of the emerging technologies that provide a powerful and supportive learning environment. According to previous studies, APAs can effectively promote learning and support social interaction with learners (Johnson & Lester, 2016; Lane, 2016). However, APAs also may cause cognitive load without providing motivational benefits in some cases and distract learners during the learning process. In other words, the results of previous studies on APAs do not provide enough evidence to argue that APA may be able to decrease cognitive load, promote motivational effects, or facilitate meaningful learning. The lack of enough evidence in the research findings seems to be variable depending upon the APA’s features, the learners, and the difficulty of the learning materials (Schroeder & Adesope, 2014). By focusing on these factors, this study provided new considerations related to embedding an APA’s role that facilitates “Word Parts” for adult students who speak English as a Second Language (ESL) with concentrating on their cognition, motivation, and vocabulary acquisition. Presenting two APA’s roles (expert model and peer model) differently influenced ESL learners’ motivation, specifically their satisfaction feelings. In addition, ESL learners’ prior knowledge affected their intrinsic and extraneous cognitive load, motivation, and vocabulary acquisition. The two different APA’s roles and their effects on ESL learners’ perceptions and learning outcomes serve as a media comparison research. Further, examining APA as a model to teach ESL students vocabulary acquisition skills serves a Computer-Assisted Language Learning (CALL) research.