Megan Hollingshead, also known professionally as Karen Thomson or by the alias Kelli Kassidi, is an established American voice actress recognized for her extensive work in English-language dubs of Japanese anime. The name Karen Thomson serves as a pseudonym, under which she has been credited for several prominent roles. Her career in voice acting began in the mid-1990s, largely in New York, where she was a regular contributor to dubs produced by 4Kids Entertainment. She later relocated to Los Angeles before eventually settling in Nashville, Tennessee.

Hollingshead's professional training and background are rooted in theatre. She studied acting at the William Esper Studio and is a founding member of the Adirondack Theatre Festival, with a stage resume that includes performances in plays such as The Duchess of Malfi and Vinegar Tom. Beyond voice acting, she is also a certified yoga instructor, a profession she has balanced alongside her work in animation and video games.

One of the key roles credited to her alias Karen Thomson is the character of Mana in the television anime series Mermaid Forest, which is based on the manga by Rumiko Takahashi. In this production, she voiced the deuteragonist, a young girl who becomes central to the story's exploration of immortality. This was part of the English dub produced by New Generation Pictures in Los Angeles.

Aside from this specific role, Hollingshead has a prolific filmography under her primary name. She is best known for voicing Nurse Joy and the Team Rocket member Cassidy in the long-running Pokémon anime series during its first six seasons, as well as the character Mai Valentine in the initial seasons of Yu-Gi-Oh! Duel Monsters. After moving to Los Angeles, she voiced numerous significant characters, including Shizune in the Naruto franchise, Rangiku Matsumoto and Nemu Kurotsuchi in Bleach, Re-l Mayer in the psychological thriller Ergo Proxy, Hilda in Eureka Seven, and Villetta Nu in Code Geass. Her work in video games is also extensive, with notable roles including the voice of Lenneth Valkyrie in the Valkyrie Profile series and Viola in Eternal Sonata, the latter of which was credited under the name Karen Thomson. She has continued to reprise her role as Rangiku Matsumoto in the recent adaptation Bleach: Thousand-Year Blood War.

Throughout her career, Megan Hollingshead has collaborated consistently with major dubbing studios and casting directors in both New York and Los Angeles. Her ability to transition between the two primary hubs of the American anime industry marks a significant achievement in her career. The use of different stage names like Karen Thomson and Kelli Kassidi has been a notable aspect of her professional profile, allowing her to take on diverse roles across various projects without being typecast solely by her most famous work.