Drogo is a powerful warlord and feared warrior. He marries Daenerys Targaryen and subsequently grows to love her. He promises to retake the Seven Kingdoms for her after she survives an assassination attempt. He raids a Lhazareen village to take slaves to fund the planned invasion. After the fight was over he was challenged to a fight by the Khal of the men in the village who believed him unworthy to continue leading the Khalasar as it appeared the Khal was obeying the orders of a woman. Drogo kills the warrior but receives a scratch to his chest and is treated by the godswife and maegi Mirri Maz Duur. His wound festers and he becomes gravely unwell. Daenerys asks Mirri Maz Duur to save him using blood magic but Mirri Maz Duur uses a spell that leaves him in a vegetative state in revenge for the destruction of her village. Daenerys ends his suffering by smothering him, then burning the body. Daenerys walks into the flames with her dragon eggs, but survives the inferno and hatches three dragons. She names the largest one Drogon to commemorate her late husband.
Drogo is a khal or warlord of the Dothraki, the famed nomadic horse-lords of the eastern continent beyond the Narrow Sea. The Dothraki are fierce warriors, skilled in battle, unrelenting in combat and known for savagery towards non-Dothraki. Amongst their own people they have a code of honor, albeit still a harsh and unforgiving one. Drogo was very young to have his own khalasar, particularly such a large one. He is a legendary warrior and has never been defeated in battle. Drogo desired the most beautiful and exotic woman in the world as his khaleesi or wife, and enlisted Magister Illyrio Mopatis of Pentos to help him find such a woman.
He is guarded by bloodriders including Qotho. Generals or ko in his khalasar include Pono and Jhaqo, men who guard him, follow him in battle and, when Drogo dies, it is their duty and honor to follow him even then to continue serving him.
Illyrio and Prince Viserys Targaryen arrange the marriage of Viserys' sister Daenerys to Khal Drogo in return for Drogo supplying Dothraki troops to support Viserys' play for the Iron Throne of Westeros. Drogo agrees, but does not stipulate a time frame. Viserys notes the length of Drogo's braid: Dothraki have to cut off their hair when they are defeated, but Drogo's long hair suggests that he has never been defeated in battle. Viserys states that Drogo is a "savage" but also "one of the finest killers alive"
Drogo marries Daenerys outside the Free City of Pentos, but is unable to communicate with his new wife due to them not sharing a language. Drogo only appears to understand the word "No" which he repeats often. A Westerosi knight who has Drogo's favor, Ser Jorah Mormont, aids with translation. Illyrio gives Daenerys three dragon eggs that have turned to stone due to the passage of time. Drogo gives Daenerys a beautiful white horse. When Daenerys wishes to thank Drogo for his gift she is informed by Ser Jorah that there is no word for "thank you" in her new husband's language, a reminder of how unpleasant the Dothraki can be. Drogo is determined to consummate their marriage immediately, which Daenerys finds uncomfortable and frightening. Attempting to make her time with Drogo more bearable, Daenerys begins learning the Dothraki language from her handmaid Irri and seeks advice from her handmaid, Doreah, on how to best please him in bed while establishing her own power over him using her sexuality. Combining these skills, she makes Drogo respect her as an equal. After two months Daenerys and Drogo are happier together. Drogo expresses satisfaction and joy at the news that Daenerys is with child, and that she thinks it will be a boy.
In King's Landing, King Robert Baratheon's spymaster, Varys, is working with Illyrio in planning the Dothraki invasion of the Seven Kingdoms. However, Drogo is content to wait until his son is born before planning the assault. Varys thinks the situation in Westeros will unravel much more quickly than they anticipated and urges Illyrio to get Drogo to speed up his timetable.
In Vaes Dothrak, Drogo is pleased to learn that his son will be the 'Stallion Who Mounts the World', a prophesied khal of khals who will command the largest Khalasar ever seen and lead the Dothraki to dominion over all the lands of the world. He also approves his wife naming him Rhaego after her slain brother, Rhaegar, a great warrior defeated in battle by "the usurper" Robert Baratheon. However, a drunken and aggressive Viserys petulantly demands that Drogo took Daenerys but never provided the army he promised. He then threatens that unless he is given his army, he will take back his sister, but leave Drogo the child that he will cut out and leave for him. Furious, but careful to control his emotions for the sake of Daenerys and their child, Drogo agrees to give Viserys a fine golden crown that others would 'tremble to behold'. Not understanding the language Viserys believes he is finally getting what he wants, and lowers his guard, allowing two of Drogo's bloodriders to disarm and restrain him. Then Drogo melts a gold belt in a pot, then 'crowns' Viserys with the molten gold, killing him.
Daenerys asks Drogo to continue with the invasion but with his obligations to Viserys gone Drogo is reluctant to attempt to cross the Narrow Sea because of his people's fear of the "poison water" (the sea, which the Dothraki fear, because they distrust any liquid that a horse will not drink) and "wooden horses" (ships). Ser Jorah later saves Daenerys from an assassin sent by King Robert. Learning of the attempt Drogo rewards Jorah with any horse he desires from Drogo's own herd. Drogo swears a blood oath that he will punish King Robert for his cowardice, lead the Dothraki beyond the poison water to invade the Seven Kingdoms and seat his son on the "Iron Chair" of Westeros.
Drogo leads his men to raid and plunder a village of the Lhazareen, peaceful sheep-herders. He plans to take slaves to trade for a fleet to invade Westeros. Daenerys protests when the Dothraki begin raping the women of the village, and has her retinue stop the practice. Mago becomes infuriated at Daenerys' presumption to give him orders and complains to Drogo.
Drogo agrees that this is custom amongst the Dothraki, but out of admiration for Daenerys' spirit, agrees to let her keep the slaves for herself. Mago accuses Drogo of being at the whim of the "foreign whore", holding his arakh to Drogo's chest. Enraged, Drogo presses the blade into his own flesh to show his contempt for Mago's challenge, causing a small flesh wound, before he fights Mago in single combat, dropping his arakh and his daggers to the ground to show his disdain for Mago's skills. He kills Mago with the reverse edge of his own weapon, and tears his tongue out through his throat. He allows one of Dany's new slaves, Mirri Maz Duur, to treat his injury – ignoring warnings from his bloodrider Qotho. The wound festers and Drogo eventually falls from his horse, unable to ride, a great shame within the Dothraki culture, for "a Khal that cannot ride cannot lead". Duur tells Daenerys that he will die soon.
The above paragraph is a scene which was made specifically for the show. A great and crucial scene which truly shows Drogo's ferocity and skill when it comes to fighting. However, in the books Khal Drogo and his Khalasar fight two separate khalasar. At the end he is victorious but has suffered serious wounds on the battlefield, enough so that Daenerys asks him to let Mirri Maz Duur to perform her magic on him, to the same result that was displayed on the show
Daenerys commands her to use magic to save Drogo and Duur agrees, but the Dothraki become agitated at this display of "witchcraft". The khalasar separates. Qotho intervenes to prevent the ritual and is killed by Ser Jorah Mormont. Daenerys goes into labor because she was shoved to the ground by Qotho.
The child is stillborn and deformed, with leathery scaled skin like a dragon's, wings, and a stomach filled with grave-worms. Drogo survives but is left in a vegetative state. Duur admits she did this deliberately in revenge for the sacking of her village. The ritual that saved Drogo drew its power from not only the death of Drogo's favored stallion but the death of Daenerys son, causing the stillbirth and monstrous appearance. Weeping, Daenerys smothers Drogo with a pillow to end his misery. She has Duur burned alive on Drogo's funeral pyre in revenge. Daenerys places her dragon eggs in the flames and then walks into them also. This conflagration triggers the hatching of Dany's dragon eggs, releasing the first three dragons into the world in a century and a half.
Daenerys sees Drogo in her visions when she visits the House of the Undying. She sees him in the tent she once shared, holding a small child in his arms, their son Rhaego. They share an emotional reunion but she chooses to leave, knowing that they are dead and only an illusion.
A fierce warrior who led a tribe of horsemen in Essos, Drogo had never been defeated in battle until he succumbed to a wound that festered after the meddling of the witch Mirri Maz Duur.