"Knowledge is power... power is power..."
In Game of Thrones, power is everything. It's why alleigances are forged, wars are waged, kingdoms are divided, and Peter 'Littlefinger' Baelish has a reason for being.
Indeed, Littlefinger is a great example of the power structure within Westeros: anyone can climb to the top of the ladder, even if you're from a nothing house in the Fingers.
Just as quickly, however, you can find it all going up in the flames of wildfire - you only need ask the hugely powerful players who were wiped off the board in Season 6: Roose and Ramsay Bolton, Walder Frey, Margaery Tyrell, and the High Sparrow.
Heading into Season 7 the balance of power has been completely shaken. The North has changed hands, Daenerys has departed for Westeros, and Cersei's claimed the Iron Throne despite having seemingly little right to do so (laws of succession don't matter when you have, ah yes, power to take it anyway). We're heading towards the endgame, which means things are really shaking up.
In the fitting (and true) words of Varys: "“Power resides where men believe it resides. No more and no less...
"Ofttimes a very small man can cast a very large shadow.” And so too can all of these.
10. Olenna Tyrell
Olenna Tyrell - played with tremendous spikiness by Diana Rigg - is one of the great verbal warriors of Game of Thrones, with few characters capable of going toe-to-toe with her in a war of words.
However, there's a lot more to the head of the Tyrell family beyond having razor-sharp wit. She's an incredibly shrewd operator who wins the game without people even realising she's been playing.
Her house's lineage has effectively been destroyed, so her long-term prospects aren't great, but heading into Season 7 she still holds a lot of power. The Tyrells have a huge army and one of the strongest fleets in the realm, are super wealthy, and have command of the Reach, a key area of Westeros. Furthermore, Olenna has lent her support to Daenerys Targaryen, and is hellbent on revenge against Cersei.
That said, though, as opposed to some others whose power in Westeros will reside because of their affiliation with Dany - even Tyrion, given his reputation in the Seven Kingdoms is mud - Olenna can stand apart; she needs Daenerys, but Daenerys will also need her, and that helps her make the list ahead of the likes of Tyrion and Varys.