This is a list encompassing the choices made in Dragon Age: Origins as well as a guide for the Dragon Age Keep. Keep in mind that some decisions made are depending on others. These dependencies are noted under their respective sections.
Dalish elf warrior or rogue. They are the member of a Dalishclan, the wanderers of Thedas, and the orphan child of the clan's former Keeper. The Dalish intend to preserve whatever they can of their old glory from the times of Elvhenan and the Dales. That is what leads Mahariel to a cave full of old ruins and a mysterious relic. It taints them forever and not even the Keeper of the clan may cure them - the only way to avoid certain death is to join the ranks of the Grey Wardens.
Dwarven commoner warrior or rogue. They are born casteless, essentially invisible in a world where rank is everything. To take care of their mother and sister, they serve the local crime lord in Dust Town. When given the chance however, they prove themselves to be a better fighter than anyone else during the Provings, which gets Brosca into a series of unfortunate events. When able, Duncan, as the Commander of the Grey in Ferelden intervenes and conscripts them into the Grey Wardens.
City elf warrior or rogue. The city elves are looked down on by most and live in extreme poverty in alienages. As such, it is far from surprising when a local lord interrupt Tabris' wedding ceremony abducting some of the females. Whether Tabris is the bride or the groom, they find their way to Vaughan. They have the chance to avenge all the abuse the city elves had to suffer from him, as well as the murder of their partner and the sexual assault of their cousin - or they can accept the lord's offer of money for his own life. Whatever is Tabris' decision, eventually they find themselves confronted by city guards who intend to take them away. Duncan steps in and conscripts Tabris saving from the injustice of the humans.
Leaving apprenticeship after succeeding at their Harrowing, they find themselves in a tough position: their friend is accused of blood magic, and have to decide if they stay loyal to their friendship or the Circle of Magi. Regardless of choice, they need to help him try and escape, after which they meet the Knight-Commander of the templars and the First Enchanter, only to realize the accusations were true. Duncan conscripts them before they would face the consequences of their actions.
Human mage. They are related to the Amells, a noble family back in Kirkwall, and thus they are the cousins of the Champion of Kirkwall, the protagonist of Dragon Age II. The same events happen to the human mages as the elven mages, and there is no significant difference made between the two throughout the story.
Noble human warrior or rogue. They are the youngest child of the Teyrn and Teyrna of Highever. Soon as their army leaves to fight against the darkspawn, the castle falls to the betrayal of the Cousland family's old friend, and most of who are in the castle are butchered. Duncan has the chance to save only the youngest child of the Teyrn, but asks for Cousland's services as a Grey Warden in turn.
Dwarven noble warrior or rogue. They are the favored child of King Endrin, much to their younger brother's jealousy. They are cast out to the Deep Roads after being framed for the murder of their older brother, while their loyal second is cast to the surface, stripped of all ranks. After they are on their own, Duncan finds them in the tunnels, recruiting Aeducan as a Grey Warden and thus saving them from the dangers of the Deep Roads.
Here you decide about the Warden's companions' fate and relationships.
(Default) No one romanced
Your Warden ignored all advances and focused on ending the Blight, rather than starting a relationship with any of the companions.
Alistair is the first Grey Warden your hero meets after Duncan, and following the Battle of Ostagar they are the only Grey Wardens in Ferelden. After all the hardship they go through and battles they fight together, bonding between the two is inevitable.
Morrigan is a witch from the Korcari Wilds, and the daughter of Flemeth, who sends her with your Warden knowing she will prove a valuable asset. Despite her acerbic nature and disapproval of love and nurture, she falls in love with the Warden.
Leliana is a lay sister in Lothering offering her help to the Warden in Dane's Refuge. In truth she is an Orlesianbard atoning for her sins in the past. After her lover's betrayal trust is hard to come by, but she feels safe and loved by the Warden's side.
Zevran is an AntivanCrow hired by Loghain to assassinate the Warden. After a failed attempt, he asks for his life to be spared, in turn he pledges himself to the hero. He stays loyal to the end, sharing a passionate relationship with the Warden.