yum, the Yellowdog Updater, Modified, is the tool that brought automatic dependency resolution and network installs to RPM-based Linux distributions, playing the same role for the Red Hat world that APT plays for Debian. An early yum HOWTO describes it as “a tool for automating package maintenance for a network of workstations” that use the RPM system, derived from an earlier tool called Yup (http://webhome.phy.duke.edu/~rgb/General/yum_HOWTO/yum_HOWTO/yum_HOWTO-1.html).
Where the underlying rpm command installs individual .rpm files but leaves you to satisfy their dependencies by hand, yum reads package metadata from configured repositories, works out the full chain of required packages, and downloads and installs them together. This is what made installing software on Red Hat and Fedora systems as simple as naming the package you wanted.
yum came out of academia rather than a vendor. The HOWTO states that “Yum was originally written by Seth Vidal and Michael Stenner, both at Duke University at the time,” and notes that Vidal later “moved to Red Hat” where he “remains the dominant force behind yum development and maintenance” (http://webhome.phy.duke.edu/~rgb/General/yum_HOWTO/yum_HOWTO/yum_HOWTO-1.html). The document describes yum as “an open source GPL project” with contributions from many developers.
yum became the default package manager across Fedora, CentOS, and Red Hat Enterprise Linux for years before being replaced by a rewrite named DNF, which carried forward the same repository-and-dependency model on a more modern codebase.