Among other things, embodiments of the present disclosure improve the functionality of electronic messaging software and systems by generating and selecting customized media content items (such as images) with avatars of different users within electronic messages based on the context of communications between the users. For example, users of different mobile computing devices can exchange electronic communications with each other, and the system can analyze these communications to present options for media content items containing the users' avatars based on content in the communications, actions or events taken by or involving the users, or combinations thereof. The users may select such media content items for inclusion in their electronic communications.