The jetifier package is a deprecated tool that helped React Native developers migrate their apps from the old Android Support Libraries to AndroidX by automatically converting dependencies' source code. It was designed for React Native projects that used native Java modules which hadn't yet been updated to AndroidX, allowing developers to keep using these libraries while their apps were AndroidX-compliant. The tool is no longer needed as modern React Native versions include AndroidX support by default and developers should ensure all their dependencies are already AndroidX-compatible.