The Beast
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
"The Beast" is a derisive nickname for the advanced battlestar Pegasus.
The name may come from the mammoth size of the ship, or the corrupt, spartan bureaucracy and overly-military attitude of its crew, originally commanded by Admiral Helena Cain.
Source: The Story So Far-SciFi.com