He is also alleged to have threatened to kill the complainant if he reported anything or tried to move to a different cell, at one point allegedly pulling a shank on the man.
Speaking to the jury of seven women and five men, Crown prosecutor Tim Bain said the case was one of "power, control, and sexual gratification, in that order".
He said Goundar repeatedly violated the complainant and used violence and threats to compel him into submission.
Bain reminded the jury they should not let the fact both men were in prison sway their judgment.
"The law doesn't stop at the gates of Rimutaka Prison," he said.
The complainant, who has automatic name suppression, began giving evidence this afternoon. An evidential video interview with police was played, during which the complainant explained he had moved into Goundar's cell in October 2017 on the promise of movies and food.
The first two nights Goundar asked for sexual favours, which the complainant refused. But on the third night he said Goundar hit and slapped him until he gave in.
Eventually the alleged abuse escalated from demands of oral sex to rape, he said.
On occasion the complainant said he would move out of the cell, and the next day Goundar threatened him with a shank, he said.
"I honestly thought that he was going to kill me right there and that was going to be my life over."
The complainant said the abuse became "routine" to the point where it was "easier to do it and get it over with".
"I got sick of getting slapped ... I would just come down and do it," he said.
In January 2018 an anonymous tip-off was made to Crimestoppers and Goundar was moved out of the cell.
In cross-examination today, defence lawyer Karun Lakshman suggested Goundar had never asked for sexual favours, nor had he assaulted the complainant.
"No, it happened exactly as I've described it," the complainant said.
Lakshman questioned why he didn't report the abuse to the prison authorities, and the complainant said he was afraid.
"You hear all the stories about snitches."
The trial, before Judge Andru Isac is set down for one week.
The earlier offending
That offending happened in late December 2011, when Goundar and his co-offender were driving in Hamilton.
The pair saw two teenage girls and stopped to offer them a lift. The girls, who did not know the men, initially refused, but were later persuaded to get into the car with the promise of food and a ride home.
He then drove them to a rural area. The girls tried to escape when the two men got out of the car to urinate, but Goundar grabbed the younger girl and forced her into the back of the car.
The other victim initially tried to get him to let go of the younger girl, but Goundar's co-offender punched her in the face, and the pair drove off with the other victim, leaving the second victim lying on the ground.
Goundar then found a secluded spot and ordered the teenager to perform oral sex on him. When she refused he hit her on the head until she complied.
She was raped and made to perform oral sex multiple times, with Goundar threatening to kill her if she did not submit.
The men eventually drove back to Hamilton East and let the girl out of the car.
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334. (available 24/7)
• Male Survivors Aotearoa offers a range of confidential support at centres across New Zealand - find your closest one here.
• Mosaic - Tiaki Tangata: 0800 94 22 94 (available 11am - 8pm)
• If you have been abused, remember it's not your fault.
• Wellington HELP has a 24/7 helpline for people who need to speak to someone immediately. You can call 04 801 6655 and push 0 at the menu.
