Massive Open Online Courses (MOOCs) attract thousands of participants who each exercise autonomy by engaging with resources and with other participants to whatever degree they wish. When analyzing participants' patterns of engagement in MOOCs, it is possible to notice that certain participants exhibit high levels of participation, actively engaging with others in forums. This study focuses on characterizing these highly active participants and understanding their contributions back to the network in a MOOC designed for teachers' professional development. Connectivism is used as theoretical lens to describe super-posters' engagement in forums. Data from participants' demographics, click data, and forum posts are used to identify these highly active users. Qualitative content analysis is used to categorize the content of their posts, and social network analysis is used to represent their patterns of engagement. Results show that super-posters are generators of engagement, repurposing the content learned from the MOOC and feeding forward new resources to the network. Results present super-posters as representatives of participation inequality in forums, in which less than 1% of participants enrolled in the MOOC contributed the most to forums. Analysis of their behavior in forums reveals super-posters as the most prestigious and most influential nodes in the networks created by participants as they engage in forums. In some networks super-posters served as bridges, connecting people from different discussion threads and helping information to flow through the network. This study provides to MOOC designers and MOOC instructors a straightforward method to identify and classify superposters in any MOOC. Findings of this study could be used by MOOC designers and MOOC instructors to develop pedagogical interventions to give these participants a special role in the next MOOC cohort, which may foster engagement in MOOC forums and nurture the cyclical process of learning described in connectivism. Regarding implications for research, this study attends to the need for qualitative methods when analyzing participants' engagement in MOOC forums and contributes to our knowledge of participation inequality. It also extends the literature of superposters by showing their characterization in a MOOC focused on teachers' professional development. Keywords: