Defoe is one of the brightest and outgoing characters in the Tottenham squad, but behind the big, bright smile there lies a pain which stems from a series of tragic deaths in his family.
Defoe's half-brother Jade was killed in a street attack four years ago, two of his grandparents passed away recently, and his father perished from cancer last summer shortly before his cousin Hannah died in an accident in St Lucia.
Football, of course, has helped Defoe attempt to come to terms with his losses, but he has recently found new inspiration from the birth of his first child Joshua-James last month.
Defoe gained a reputation as a bit of a playboy during the early stages of his career, but the responsibility of fatherhood appears to have given the 30-year-old a new outlook on life.
"It's amazing. It's hard to put into words what it feels like," the Spurs striker said.
"It changes your mentality, the way you think. Last year was a difficult time for my family. Losing people close to you is difficult. But in a way I feel I'm blessed because when you lose people God gives you someone else.
"We have another little Defoe in the family. I think about my Dad, my Nan, my brother, my cousin every day, and that is why when I do things, I do them properly.
"I was down recently when I suffered an injury, but I've been through a lot and I knew I had to bounce back, come back stronger and help the team.
"It does make you think you want to do well for the people you have lost, and I have a little boy now, so I want to work hard to be a better person and keep on doing what I'm doing."
Defoe's new mature approach does not stop him from poking fun at another member of the Tottenham squad who has just become a parent for the first time - Gareth Bale.
Bale will look to tear Inter Milan apart for a third time in as many years on Thursday, but when he gets home he, like Defoe, will be changing nappies and feeding his young child Alba Violet Bale, who was born last October.
That the initials of Bale's newborn match those of the Tottenham manager Andre Villas-Boas has made him the butt of jokes from his team-mates, Defoe revealed.
"He has little AVB, little Alba," Defoe said.
"I give him stick about it. Gaz is the first one to be on someone, giving them banter so if you have a chance to get it back you have to take it."
Defoe's smile disappeared immediately when the topic of potential racist chanting during Thursday's last-16 first leg was raised.
Last month Inter were fined £43,200 after their fans hurled racist abuse at former player Mario Balotelli during the first Milan derby since he joined bitter rivals AC Milan.
Defoe was racially abused against Italian opposition earlier in the Europa League when Spurs played Lazio and he is disappointed that black players are still targeted because of the colour of their skin.
He said: "It is really disappointing. It seems to be happening a lot.
"I am doing my job and trying to win a game for my team. I shouldn't be getting racially abused, it's silly."
AC Milan midfielder Kevin-Prince Boateng walked off the pitch during his team's friendly against Pro Patria in January after he was racially abused, but Defoe is unsure if he would take the same course of action if he was targeted on Thursday.
"I only found out what was happening after the Lazio game," Defoe said.
"I was upset. If it happens again I will speak to people at the club, but I have to try not to let it affect me when I am playing.
"Obviously Prince Boateng decided to walk off. I don't think it's something that I would do, but saying that, you don't know how you'd feel at the time."