Callisto
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Callisto was the lover of Kassia and a native of New Caprica. He died during a Cylon atack on that colony, and his body was taken by the Cylons for experimentation. His loss permanently affected Kassia.
Note
The "Battlestar Galactica" video game has its own continuity that uses elements from both the Original Series and the Re-imagined Series.