Ralof is a Stormcloak Soldier in The Elder Scrolls V: Skyrim. He is the first character to directly speak to the Dragonborn during the game and one of the two soldiers that follow alongside the Dragonborn during the Skyrim Civil War, the other being Hadvar of the Imperial Legion.
Ralof and his sister Gerdur live in the small town of Riverwood just south of Whiterun. The two are often considered the town's leaders.
It is also implied that he and Hadvar actually knew each other before the war, as implied by a conversation they have before they retreat inside the nearby barracks.
Ralof is the first character that speaks to the Dragonborn over the course of the game, he reveals in the intro that the two of them, Ulfric Stormcloak, and a horse thief named Lokir are being transported to Helgen and awaiting execution (even though both Lokir and the Dragonborn's crimes aren't punishable by execution). Upon arriving, Lokir is killed while attempting to flee and Ralof, the Dragonborn, and Ulfric witness the execution of one of the Stormcloak soldiers. The Dragonborn is then called up to the chopping block, but before he/she is supposedly beheaded, a black dragon arrives and destroys Helgen, killing most of its inhabitants in the process. Fortunately, Ralof, Ulfric, Hadvar, General Tullius, and the Dragonborn escape alive, but it also resumes the Skyrim Civil War.
The Dragonborn can choose whether to follow him or Hadvar into a nearby barracks and escape from it. Afterwards, he will tell the Dragonborn to meet him in Riverwood, where he tells his sister and brother-in-law about the dragon attack. They tell the Dragonborn to travel to the city of Whiterun and speak to the Jarl about the attack.
The Civil War will resume as a result of the dragon attack. If the Dragonborn decides to join the Stormcloaks, Ralof will be in the presence of the Dragonborn over the course of the war, assisting him/her at the Battle of Whiterun, ambushing a cart full of necessary supplies in the Reach, and rescuing Stormcloak prisoners from a fort in Falkreath. He can often be found at the tavern at Riverwood in between battles and after the war ends.