The Killer Whale was first introduced as one of Zebra's neighbors, hunting the seals next door. After several unsuccessful attempts, he was given a meatloaf that turned out to be a bomb that was meant for Pig. He died. The Killer Whale came back to be in Rat's baseball game, but he was killed off-panel again because he was supposed to be dead. He then came back to life to eat the Killer Dolphins.
The Killer Whale was a Killer Whale whose goal was to eat John and Jennifer Seal. He tried to be nice, but really he wanted to devour John and his wife.
John and Jennifer were the prey of the Killer Whale, and they were smart and knew how to avoid him, like Zebra and the Crocs. They avoided him, but at one time The Killer Whale asked why he was stopped by a glass window from killing the seals, which hurt Stephan Pastis' feelings.
Apparently, Zebra could maybe like the Killer Whale, as he gave a meatloaf to him, not knowing it was a bomb.
The Killer Whale may have a family, or at least one child, as he was selling cookies for his kid's fundraiser.