Sovek

Logical. As logical as the Vulcans on the planet he hails from.  Sovek lived upon Vulcan in her early days, before the Vulcans became  logical. Back then he was as passionate as the beings he knew. But as  time went on, this soft, parasitic canine creature found that he felt  alone. His life span stretched on longer than any Vulcan he knew. He  grew desolate and afraid, finding comfort in the Vulcan pottery and  stoneware he curled up in, hiding in the hot, dry, lonely mountains and  scrags of Vulcan. The pain he felt manifested in the heart shaped crack  on his chest, the first testament to his strong feelings. As time went  on, he seemed to remain alone, cracking and pained, foliage growing from  the cracks in his potter. Finally, one day in the 4th century of  Vulcan, a being found him, hiding and alone. "Do not be afraid, for fear  has no logical grounds," a soft voice said to him and lifted him out of  the misery. Surak mind-melded with him and showed him how to save  himself through logic. From that day on, Sovek became a follower of  Surak and the way of logic, and has remained that way ever since. As  time went on, Surak eventually passed but Sovek lived on, his life  stretching farther and farther through time, even longer than the  long-lifed Vulcans.

He first heard of a Vulcan and human match the day of the birth of Spock. He was curious as to what would  possess a logical Vulcan to marry and produce heirs with a human, and  kept a careful eye on the progress of this young child. As Spock grew,  Sovek remained his silent and hidden watcher, studying him and trying to  understand this halfling. When Spock decided to join Star Fleet, Sovek  managed to make his way to Earth, only to remain grounded as Spock took  flight aboard starships. For many years his only knowledge of Spock's  progress came from hiding and listening in and spying at Star Fleet in  San Francisco to find out more about his subject of interest, and the  few times when he could catch Spock on Earth.

One day,  he finally met him though. Spock's friend, Capt. James T. Kirk came upon  Sovek and through a 'meeting of the minds' came to understand what  Spock meant to Sovek. Kirk snuck him aboard the Enterprise and brought  him to Spock, stating there was someone he needed to meet. Sovek had to  overcome many emotions at this, finally being able to mind-meld and  'speak' to this Vulcan halfling he had invested so much energy and  concentration in. They became the Vulcan equivalency of friends (in  Sovek's mind. To Spock, they were friends, plain as that) Sovek keeps to  Spock's quarters for the most part, hiding himself from the curious  crew except for Spock's closest friends. He has grown quite fond of  Nyota Uhura, who in return sneaks him treats, which he considers  logical. 

Spock's human-ness has begun to rub off on him  as he learns the logic behind it all, though he still holds fast to the  memory of Surak, the Vulcan he considers his first real companion.