To Khal Drogo
To Khaleesi Daenerys Targaryen
Realizing that she needs to motivate her new (and enormous) khalasar into waiting until they have enough ships to take them to Westeros, Daenerys rides Drogon before them. She reminds them that she has yet to select her three bloodriders, as all khals have done before her. She then declares that she is not a khal and selects the entire khalasar her bloodriders.
In the books
In the A Song of Ice and Fire novels, the title of bloodrider carries great prestige within a khalasar. Bloodriders sit next to the Khal in feasts and ceremonies. They may also share the Khal's wife (depending on the personal preferences of the khal in question), but never his horse. A bloodrider may also be a ko, commanding a subdivision of the khalasar.
Daenerys' bloodriders are Aggo, Jhogo and Rakharo. So far in the books they are all alive and well.