Isis

Isis was a shapeshifting alien introduced in the Star Trek episode Assignment: Earth. She could assume a humanoid shape, but most often would assume the shape of a black Terran cat.

In human form Isis was portrayed by Victoria Vetri, and in feline form by three different cats.

Isis accompanied Gary Seven to Earth in the year 1968. After helping Seven escape from the Enterprise Isis beamed with him to New York City on Earth. She assisted Seven in sabotaging an orbital nuclear defense platform, which Seven caused to veer off course and detonate 104 miles above Earth. This helped convince Earth governments to stop putting nuclear weapons into orbit.

She later traveled with Seven and Roberta Lincoln to the 23rd century to keep a rogue Ageis agent from assassinating Captain Spock in 2293. Afterwards she returned with Seven and Lincoln to the 20th century.

Over the next two decades Isis played a key role in defeating Khan Singh. Seven had her work under cover as a woman named Ament, and she managed to become Khan's most trusted advisor. Meanwhile she transmitted crucial intelligence back to Seven and Lincoln.

After Khan and his fellow augments were defeated, they were taken aboard the SS Botany Bay. Isis apparently died by throwing herself in the path of a knife thrown by Joaquin Weiss at Lincoln. Khan offered Joaquin's life to Seven, but Seven refused to stoop to his level and had Joaquin put in a stasis pod with the rest of Khan's people.

Later Isis, or someone just like her, accompanied Gary Seven on his later visits to the Enterprise

Trivia

 * While The Rise and Fall of Khan Noonien Singh, Volume 2 had Isis dying as described above, subsequent works showed Seven traveling with another black cat named Isis. It was unclear if Isis had been resurrected, someone else took her place, or if Isis was from a different time period.