The expansive universe of Star Trek has not only given us unforgettable stories and characters but also some of the most surprising and impactful guest star appearances in television history. These guest stars have left an indelible mark on the Star Trek universe, enriching its lore and bringing depth to its already complex narrative. Here’s our list of the top 5 unforgettable guest stars from the Star Trek series, counting down to the most memorable.

5. Stephen Hawking in Star Trek: The Next Generation - "Descent, Part I"

Having one of the most brilliant minds in history appear on The Next Generation was a treat for fans. Stephen Hawking made a historic cameo as himself, joining a holodeck simulation with Albert Einstein, Isaac Newton, and Data for a game of poker. It was a humorous and profound moment, symbolizing the bridging of science fiction and reality in a way only Star Trek could achieve. Hawking’s appearance remains one of the most iconic moments in the series, celebrated for its wit and the sheer delight of seeing Hawking interact with some of history's greatest minds... and an android.

4. Joan Collins in Star Trek: The Original Series - "The City on the Edge of Forever"

In one of the most beloved episodes of The Original Series, Joan Collins guest-starred as Edith Keeler, a compassionate social worker in the 1930s. Her performance added depth to a tragic love story between her character and Captain Kirk, set against the backdrop of time travel and the moral dilemmas it entails. Collins' portrayal of Keeler was both heartwarming and heartbreaking, providing Star Trek with one of its most poignant episodes and showcasing the series' ability to tackle complex themes with sensitivity and depth.

3. Whoopi Goldberg in Star Trek: The Next Generation

Though Whoopi Goldberg became a recurring character as Guinan, her initial appearances were nothing short of guest star spectacles, thanks to her celebrity status at the time. A lifelong Star Trek fan, Goldberg's portrayal of the El-Aurian bartender brought a mysterious and calming presence to the Enterprise, offering wisdom that often guided the crew through moral and philosophical dilemmas. Her unique perspective and backstory added layers to the Star Trek universe, making her debut one of the most impactful in the series' history.

2. Leonard Nimoy in Star Trek: The Next Generation - "Unification I & II"

Leonard Nimoy's return as Spock in The Next Generation was a monumental event, bridging the gap between the original series and its successor. His quest for Romulan-Vulcan reunification added a significant chapter to Spock's story, blending the old with the new in a tale of diplomacy and intrigue. Nimoy's performance was a poignant reminder of Spock's enduring legacy and the ideals Star Trek represents, making his guest appearance a standout moment in the franchise.

1. Jeffrey Combs across various series

Perhaps no other actor has left as indelible a mark across the Star Trek universe as Jeffrey Combs. With roles ranging from Weyoun, an enigmatic Vorta in Deep Space Nine, to the Andorian commander Shran in Enterprise, Combs has portrayed an astonishing range of characters, showcasing his versatility and making each role memorable. His performances have been pivotal, enriching the Star Trek lore and making him a fan favorite. Combs’ ability to bring depth and complexity to every character he plays secures his place at the top of our list.

These guest stars have not only contributed memorable performances but have also deepened the richness of the Star Trek universe, leaving a lasting legacy that continues to inspire and entertain.