Caster

Caster is an obsolete term that used to refer to the player who cast a spell. In general, cards that were printed with the term "caster" have received errata in the Oracle card reference to say "controller"

From the glossary of the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

Caster (Obsolete)

An obsolete term that referred to the player who cast a spell. In general, cards that were printed with the term “caster” have received errata in the Oracle card reference to say “controller.”