The "Owner" field in a work request identifies who (or what) is doing the work to resolve the request. An owner is either a UW userid, or an e-mail address of another work tracking system, typically "request@ist".
This is distinct from who/whatever is responsible for the resolution of that work; that's recorded in the responsible field.
When there are multiple owners, the extra names in the list identify those who may be advising, or in fact doing part of the work best suited to their skills and availability. Regardless of their contribution, it's the first person/system in the list who is currently doing the work. That name may change over time.
When specifying this field in a customized sort or display, any of the names "owner" or "Owner" can be used.