Jeri Ryan wasn't the first choice but was the right one to play Seven of Nine in Star Trek: Voyager

Star Trek: Voyager benefited from the arrival of Jeri Ryan to the cast. The show was doing fine, but Ryan's addition at the end of season three and the start of season four added a huge jolt to the system for the show. They rightly choose to move on from Jennifer Lien, and her character of Kes, while giving Ryan a bulk of the season to develop her character.

Ryan's character was that of Seven of Nine. A former Borg drone, whose real name was Annika Hansen. A young woman from Earth, whose parents brazenly attempted to learn more about The Borg, long before anyone had an idea of what they were capable of. Due to that, she and her parents ran afoul with the Borg, and Annika became a Borg designated Seven of Nine of Tertiary Adjunct of Unimatrix Zero One.

Ryan's arrival and her role in the show brought new life to the series. Her provocative attire and unique personality really enticed fans old and new to watch her character. It wasn't just Ryan's good looks that brought and kept fans in. It was her brilliant melding of character traits. On one hand, she was a lot like Spock. Efficient, assertive, confident, and bold. Yet, in many ways, she was still just the same child that the Borg took. Petulant, argumentative, scared, and at times, lost.

It was the brilliant dance that Ryan did with the character's emotional center that made fans come for the sex appeal but stay for the emotional conflict. The growth and development of the character was a major component in later seasons. While she didn't develop as much emotionally as say The Doctor, she did develop enough that fans stayed invested in the character.

This was probably the right move, as it gave The Doctor and Seven of Nine a uniqueness that didn't interfere with one another.

While there was another in line for the role, Susan Gibney, Ryan was the right call. Gibney had already had a turn with Star Trek, and while she did fine, she didn't have the raw charisma that Ryan did. That charisma translated well on screen, and without it, who knows if the show would've used the character as well as it did after her initial debut.