A Quarren neuropathology expert who ran the memory-altering treatment used to turn abducted aliens, including Voyager's crew, into workers.
Kadan is a leading Quarren neuropathologist in Workforce and Workforce, Part II. Officially he treats people diagnosed with dysphoria syndrome, a supposed condition involving confused memories, but the treatment is the means by which abducted aliens are conditioned to believe they are Quarren citizens and assigned jobs at places such as the energy plant where Janeway now works.
When Tuvok resists his conditioning and keeps insisting he belongs elsewhere, Kadan's treatment is used to suppress him. Kadan is protected by powerful allies, and exposing his role becomes key to freeing Voyager's crew from the scheme.