The first image depicts Emma D'Arcy as Princess Rhaenyra Targaryen and Matt Smith as her uncle, Prince Daemon Targaryen. The story opens with the death of Rhaenyra's mother Aemma, leaving her father, King Viserys I Targaryen (Paddy Considine, not pictured) in a bind as the realm prefers men to inherit the Iron Throne. However, Viserys's younger brother Daemon is flighty, quick to anger and Viserys fears he would embroil the realm in costly and unnecessary conflicts, whilst Rhaenyra is studious, serious and, in her father's eyes, more capable of ruling.
The second image depicts Olivia Cooke as Lady Alicent Hightower and Rhys Ifans as her father, Otto Hightower, Lord of Oldtown and Hand of the King. Alicent may be the most eligible bride in the Seven Kingdoms and with the queen deceased, Lord Otto hatches a scheme to marry his daughter to the grieving king to cement his house's power. Alicent and Rhaenyra are on friendly terms, but the prospect of Alicent having children whose legitimacy might threaten both Rhaenyra and Daemon's claims to the throne drives a wedge between them.
The third image depicts Lord Corlys Velaryon, Lord of Driftmark and Master of Ships on the small council. A formidable sailor, explorer and warrior, descended from ancient Valyria, Corlys has sailed to the very edges of the known world, to distant Ib and Nefer on the Shivering Sea, to Cannibal Bay at the howling edges of the northern icepack and to distant Asshai-by-the-Shadow, on the far side of the Jade Sea. Though his exploring days are behind him, Corlys has used his immense wealth to make his family the richest and most powerful in Westeros, even eclipsing the Lannisters of Casterly Rock. A friend and ally of Prince Daemon, as well as Princess Rhaenyra's prospective father-in-law, he is poised to become the most powerful man in the Seven Kingdoms behind only the king, and whomever he backs in the ensuring struggle for power will have found themselves a vital ally.
The images seem to come from a later point in the storyline (as Alicent and Rhaenyra are much younger at the reported start of the story, unless they are completely changing the timeline), presumably scenes from later in the first season they are shooting first for practical reasons.
House of the Dragon is currently shooting on location in Cornwall. The series is expected to air on HBO and Sky Atlantic early in 2022.