The wealthy American dentist who killed Zimbabwe's beloved lion Cecil was a trophy-seeking bow hunter with a poaching conviction in the United States.

Walter Palmer, 55, boasted that he is a bow hunting purist who doesn't carry a gun as backup when pursuing big game.

A figure of some renown in hunting circles, he made the claim when in a New York Times article on trophy hunting published in 2009.

He told the paper he learned to shoot at age five and has now slain all but one of the 29 trophy animals recognized by the bow hunting group Pope and Young.

Palmer is said to be able to hit a playing card with his compound bow from 100 yards (meters).

Images of Palmer grinning over his dead prey -- a limp leopard held up like a plush toy in his shirtless arms, a rhino, an elk, a big horned sheep, a cape buffalo -- circulated widely on the internet and fed a firestorm of criticism.

In 2006 in the United States, Palmer illegally shot a black bear outside a designated hunting zone. He was later convicted of lying to federal authorities about the location of the kill.

His kill list of 43 different animals also includes a polar bear, mountain lion, an elephant and an African lion he killed in 2005, according to club records obtained by the Minneapolis Star Tribune.

Cecil, a popular attraction among many international visitors to the Hwange National Park, was reportedly lured outside the park's boundaries by bait and initially shot with a bow and arrow.

But the arrow is said to only have wounded him and a conservation charity said it was 40 hours before Palmer and his guide tracked Cecil down and shot him dead with a gun.

Officials in Zimbabwe -- who are pursuing poaching charges against professional Zimbabwean hunter Theo Bronkhorst and local landowner Honest Ndlovu -- said Palmer paid $50,000 for the hunt.

- 'I had no idea' -

Within hours of the news breaking Tuesday, Palmer's social media feeds were flooded with blistering attacks -- and threats.

The Facebook account of his dental practice -- River Bluff Dental in a suburb of Minneapolis, Minnesota -- was shut down and its website kept crashing.

His Twitter account appeared to have been hacked as it was filled with images from the Lion King movies and missives like "You people seriously need to chill out. It was just a lion. Our practice is our livelihood."

By Wednesday morning a petition demanding justice for Cecil had garnered more than 400,000 signatures and there were more than 6,200 messages about his practice on review site Yelp.

A makeshift memorial had also formed outside Palmer's shuttered office after people dropped off stuff toys and flowers, images posted by local media showed.

Palmer expressed regret at killing Cecil Tuesday, insisting that he had "relied on the expertise of my local professional guides to ensure a legal hunt."

"I had no idea that the lion I took was a known, local favorite, was collared and part of a study until the end of the hunt," Palmer said in a statement.

"I deeply regret that my pursuit of an activity I love and practice responsibly and legally resulted in the taking of this lion."

However, critics were unmoved by his apology. Many attacked him for engaging in the controversial sport to begin with. Others questioned his sincerity given his past poaching conviction.

Palmer pleaded guilty in 2008 to poaching charges after killing a black bear some 40 miles (64 kilometers) away from his designated hunting zone and then lying to officials about it, court records obtained by AFP showed.

He paid a nearly $3,000 fine -- the value of the slain bear plus the standard fine -- was placed on probation for a year and required to surrender the animal's remains.

A profile on his dentistry practice's website said the married father of two is originally from North Dakota and "enjoys all outdoor activities."

"Anything allowing him to stay active and observe and photograph wildlife is where you will find Dr. Palmer when he not in the office," it continued, without mentioning his hunting exploits.