After rowing off into the night in Season 3 of Game of Thrones, blacksmith (and bastard son of Robert Baratheon) Gendry disappeared from the show. Though fans wondered where he was, the show provided no answers until Season 7's "Eastwatch." Gendry returns to Game of Thrones, and he couldn't be more welcome.
It turns out that Gendry was not, as actor Joe Dempsie once joked, "still rowin'" after all these years. He had pulled ashore in King's Landing and set up shop, making the most of his trade as a blacksmith. However, he was far from satisfied with this. The Lannisters had killed his father and tried to kill him, way back when Joffrey was slaughtering all of Robert's bastards. King's Landing would have been a dangerous place for Gendry if anyone knew who he was, and he was ready to move on.
Luckily Davos was there to offer him the opportunity. He planned to take Gendry along to Dragonstone, then send him off to Winterfell to work in the forges there. However, Gendry had other ideas: he made himself available to Jon as an ally, and he could prove to be a useful one considering his skill set. Late in the episode Gendry heads beyond the wall with Jon and company, but if he makes it back, he could get to work making all those dragonglass weapons everyone will need when the White Walkers attack. In the meantime, he's pretty good with a hammer.
After such a long absence, fans were delighted to see Gendry on their screens again. As one of the few people in Westeros who wasn't morally bankrupt and cruel, Gendry was always a pleasure to watch, and he endeared himself to viewers even more through his bonding with Arya Stark while they were on the road together. He'll be a good ally for Jon not only because of his talents, but because he's a trustworthy person.
Game of Thrones is well versed at sending away beloved characters without revealing what happened to them, then springing their return on audiences out of the blue. Much like the Hound's reappearance in Season 6, Gendry showing up again in Season 7 Episode 5 was an exciting way of making it clear that everything is coming full circle as the series nears its end. All the loose ends are being tied up.
Gendry may have been gone for years, but he's already making up for lost time by joining the war efforts against Cersei and against the White Walkers. He definitely has a role to play in the coming battles, and it's sure to be an important one.