It affected him so much that 47 years later, the actor from Kairaki Beach near Kaiapoi still plays the iconic Star Wars screen character as he brings joy to terminally ill patients of all ages.
"A lady in her 70s was a major fan. She had planned her funeral right down to the smallest detail for a Star Wars-themed farewell," David said.
"Her family invited me to see her shortly before she died, and when I went into the room dressed up as Vader, she had a huge grin ear to ear on her face.
"We chatted about how much of a fan she was, then I left and she passed shortly after.
"It was so emotional but a great honour to make her happy at the end."
His first call to help came one night when a family contacted him and asked if he could come down to visit their terminally ill son.
"Tomorrow?’’ inquired David. "No, now please," they replied.
"It was a very intense session because nothing prepared me for it. But the little boy was such a big fan.
"He was so sick he could only whisper.
"We had this wonderful conversation about his passion for Darth Vader.
"I left him with one of my replica gloves as a memory. They buried it with him."
Four times David has been asked to visit people at the end of their lives.
"If I can help in some way then that’s what I love doing."
The most noted point about his portrayal of Darth Vader is that he does it for free.
"If I can make a difference and put a smile on someone's face, then that’s all I need.
"I have trained myself over the last 17 years to become the character, and it takes every ounce of that training to remain in character as I listen to the last words of a young person with only a few hours left."
David said he was bullied at school and after watching Star Wars he became obsessed with Darth Vader.
"Here was a guy who stood up to everyone. He became my inspiration."
David has spent almost $14,000 assembling the costume, locating many rare and unique elements of it from around the world.
He said it was a very physically demanding costume to wear at events, such as Santa parades and Armageddon shows.
"It’s heavy, weighing about 26 kilos.
"It’s a beast to wear when it’s hot outside."
He once collapsed from heat exhaustion at a New Brighton parade so he doesn’t do them any more.
"I had to stop attending shows because over-excited fans started damaging the suit. But now I have found my calling helping others."
The unemployed actor said it was his passion now.
He said when he started wearing the costume, people quickly recognised the character.
"Surprisingly people flock to meet and be photographed beside the most famous movie bad guy.
"Put me next to someone dressed as Han Solo and they all come over to me."
Now David spends his days helping others.
He often receives requests for video messages in costume for sick children or fans in America, and he said he is always available for those who need him.
"Recently I was making preparations for my mother's funeral when the undertaker inquired if I was available for themed funerals. I said yes, even if it is simply greeting guests or handing out programs for fans of the popular film franchise."
