This study presents a theory about dynamic game characters within a broader character ecology in which characters are constantly produced and reproduced in a variety of media. Characters do not appear only in games, they migrate from one medium to another. They are independent from any medium in particular: a character does not require a specific medium to come into existence. Authoritative forces try to shape the overall interpretation of circulating characters transmedially in comics, television series, films, games and more through different venues of control, such as authorship, canonisation and ownership or intellectual property. This study addresses the struggle for interpretive authority by explaining how the player constructs the identity of dynamic game characters in digital games, and by discussing how dynamic game characters connect to and influence other character manifestations within a broader media ecology in which characters circulate. The research question of this study is: What are dynamic game characters? Through reader-response theory adapted for cybermedia phenomena such as games, this study approaches characters as a player-constructed phenomenon, in which the game character needs the player in order to be invoked, but the game encourages the meaning-making process with different means to different effects. Dynamic game characters are those game characters whose development structures branch into different outcomes, each of which are undetermined until the player actualises one or more possibilities that steer that direction onto distinct paths with a specific outcome. Dynamic game characters have become a phenomenon that challenges practices of (trans-)media control. A theory of dynamic game characters tells us about the migration of entities via different works, and how the perceiver comes to understand them within a context saturated with characters, stories and a variety of media platforms. Digital games are just one of the many media platforms that participate in this character ecology, and they allow characters to challenge the idea that within a single piece of work the character must maintain a linear, continuous and coherent identity that stretches the understanding of characters as authored and predictable within a single work. This study argues that dynamic game characters are a type of quasi-person in digital games whose development consists of multiple outcomes. Digital games accelerate a dynamic game character’s identity within a single work, unlike non-cybermedia in which a character’s identity is constructed over multiple works. They challenge venues of control, because the player has creative agency over the dynamic game character’s characterisation process within a single work. However, once dynamic game characters transfer to other works, authoritative institutions break the player’s participation in the dynamic game character’s development. These transfers sacrifice player participation to create the illusion of a coherent identity between the manifestations of the character over multiple works.