Both the owner and his pets had abusive pasts.
He struggled with anger management issues, and was involved in fights and secret societies.
The dogs he cares for now used to be malnourished and were kept in overcrowded cages by their previous owners.
Today, man and animals are trying to deal with their unhappy histories so that they can bring joy to others through pet therapy.
Derrick Tan, 33, is head of operations at Sunny Height, a pet daycare centre.
Last Thursday, 19 seniors aged 60 to 81 from the Geylang East Home for the Aged, Social Day Centre, went there to cuddle 20 dogs.
The idea is that playing with these animals would benefit the elderly emotionally and socially. It was their third time returning for pet therapy, as the seniors had given feedback that they enjoyed the sessions.
Mr Tan is also president of Voices for Animals (VFA), a rehabilitation society for former breeding dogs and cats. It provides pet therapy sessions and has worked with the elderly and people with special needs.
He said: "We believe in the healing power of love. We try to help mostly those animals that are waiting for their time to go, those that are helpless and those that people don't really pay attention to.
"I strongly believe in pet therapy. There's something about loving an animal and the way it loves you back unconditionally. It calms you down and it heals both ways."
VFA has saved about 80 dogs and cats from puppy mills and breeders. Some were rescued off the streets.
He said many were severely underfed, some had skin diseases and heartworms, and some had renal and liver failure.
It is hard to imagine that Mr Tan was once a self-professed "Ah Beng". The heavily-tattooed man admitted to The New Paper that when he was 14, he was involved with secret societies.
But all that has changed - now, together with the animals VFA saves, Mr Tan plans to give back to society, one cuddle at a time.
With a white dog on his lap, former boxer Michael Loh, 79, said: "I used to have a dog just like this named Baby and I loved her very much. Dogs are very smart and intelligent creatures."
After an earlier pet therapy session, Soh Yin Leng, 75, felt so comfortable with the dogs that she even wanted to swim with them in the pool meant for dogs.
She said: "I told everyone I would bring my bathing suit this time round so I can swim with the dogs and play with them more."
The dogs did take a dip in the pool but unfortunately, because of the heavy rain and the cold weather, it was unsafe for Madam Soh to swim.
Although she was disappointed, she said: "I'm not afraid of the dogs. When you carry them, they feel warm in your arms and it feels like carrying a baby."
After the three-hour event, Mr Tan said: "Just a pat on the back or handshake, or the elderly saying 'Thank you for loving us' is enough. Nothing else can buy that kind of satisfaction."
This article by The New Paper was published in MyPaper, a free, bilingual newspaper published by Singapore Press Holdings.