Roku fell for Ta Min when he was a child but he was too afraid to speak to her and eventually had to leave the Fire Nation and go master the other elements. After twelve years, he eventually returned and still had feelings for her. At some point, he and Ta Min got married. Roku explained to Aang that he was persistent and eventually won her heart. Together, they had a daughter named Rina and lived with a small village on a volcanic island. At some point, the volcano started to erupt and Ta Min evacuated with the entire village while Roku attempted to stop the flow. However, after being betrayed by his friend Sozin, Roku was killed by the volcano and left Ta Min to live the rest of her life as a widow.
Roku is a somewhat popular character in the Avatar fandom. All avatars have at least some amount of popularity and Roku is no exception. Many fans love the episode that covered Roku's life and some wanted to know even more than what they were shown. A lot of fans loved the fact that Roku turned out to be Zuko's maternal great-grandfather. Some fans like to pair Roku with his wife Ta Min but many love to pair him with his childhood friend Sozin.
Rina is the daughter of Roku and Ta Min. She eventually moved to the town of Hira'a on the outskirts of the Fire Nation. There she eventually married Jinzuk who was the magistrate. Together they had a daughter named Ursa. They lived a happy life until Prince Ozai arrived to propose to Ursa. They married and after the wedding, Rina was never allowed to see Ursa again. She and Jinzuk eventually passed away before Ursa was finally able to return to Hira'a.
Roku is the only avatar to appear in an elderly form when called upon by the current avatars as all others appear in their primes.