Stamford, Conn. ? Travis the chimpanzee, a veteran of TV commercials, was the constant companion of a lonely Connecticut widow who fed him steak, lobster and ice cream. He could eat at the table, drink wine from a stemmed glass, use the toilet, and dress and bathe himself.

He brushed his teeth with a Water Pik, logged on to a computer to look at photos and channel-surfed television with the remote control.

But on Monday, the wild animal in him came out with a vengeance.

The 200-pound animal viciously mauled a friend of his owner before being shot to death by police.

Investigators are trying to figure out why — whether it was a bout of Lyme disease, a reaction to drugs, or a case of instinct taking over.

“It’s hard to say what exactly precipitated this behavior,” said Colleen McCann, a primatologist at the Bronx Zoo. “At the end of the day, they are not human and you can’t always predict their behavior and how they or any other wild animal will respond when they feel threatened.”

Travis attacked 55-year-old Charla Nash as Sandra Herold frantically stabbed her beloved pet with a butcher knife and pounded him with a shovel. Nash was in critical condition Tuesday with “life-changing, if not life-threatening,” injuries to her face and hands, Mayor Dannel Malloy said.