Jarilo is understood in modern scholarship as a Slavic god of vegetation, fertility, spring and war, but with an important qualification that must come first: he is not securely attested in the medieval written record, and his profile as a god has been reconstructed by scholars from folk songs, seasonal rituals and comparative evidence rather than read directly from any early source that describes a deity of this name. The name Jarilo (and its variants) is preserved above all in the ritual folk customs of the Slavic countryside, particularly in the spring festivals recorded in more recent centuries, in which a figure called by such a name is welcomed, celebrated and then ritually mourned or buried as the season turns.
From these customs, and from comparison with better-attested Indo-European and Baltic material, scholars, notably Radoslav Katicic and Vitomir Belaj, have proposed that behind them lies an old myth of a seasonal deity: a young god associated with the fertility of spring who arrives, is united with a goddess, and is then killed or dies as the year moves toward winter, to return again the next spring, in the widespread pattern of the dying-and-returning vegetation god. This is a plausible and influential reconstruction, but it should be presented honestly as a scholarly hypothesis built from later folklore and comparison, not as a directly documented ancient cult. Jarilo is best understood, therefore, as a figure recovered by modern research into the seasonal rituals of the Slavs, a probable god of the spring and its fertility whose worship is inferred rather than recorded, and around whom real scholarly debate continues.