In patch 0.5 for Path of Exile 2, Return of the Ancients, you'll be able to specialise your endgame mapping experience by selecting special Atlas Masters that enhance your strategies.

Jado, Doryani & Hilda

Jado, Doryani & Hilda
The Masters of the Atlas are NPC characters that essentially act as a form of Atlas Tree Ascendancy, allowing for another layer of gameplay customization in the endgame. In patch 0.5, there will be 3 Masters that can provide their exclusive bonuses: Doryani, Hilda and Jado.
During progression of the Atlas, you'll encounter these NPCs who will task you with completing various quests. For example, Jado will enlist your services to seek out powerful artifacts on behalf of the Order of the Djinn. Upon completing these quests you'll unlock nodes in Jado's Atlas Master Ascendancy, which you can then choose to apply to areas you open from the map device.
Each Atlas Master has a total of 12 nodes made up of 4 rows with 3 choices in each row. You'll be able to acquire 4 points to place in these nodes, so you'll be able to apply up to 4 nodes to your maps.

Four Nodes Selected on Jado's Spycraft Ascendancy
Each Master of the Atlas has their own specialisation to boost specific areas of gameplay and enhance certain strategies. However, you can only select one Atlas Master to apply their bonuses to your maps at any one time, but note that it's free to switch between Atlas Masters when opening a new zone.
Jado's Spycraft is an Atlas Master Ascendancy with a focus on in-map mechanics and layout manipulation. One first-row node option will massively improve the chance of Strongboxes in your maps being Unique Rarity, whilst also making more Rare Chests appear too. Another option in the first row will cause map bosses to drop an additional Unique item.

In The Wrong Hands, Jado's Spycraft first row option
However, one of the true strengths of Jado's Atlas Master Ascendancy is zone manipulation, with one option causing Corrupted Waystones to open portals to a random map layout, allowing you to potentially reroll an unfavourable layout into something better for your strategy.
As a member of a guild of Monster Hunters, Hilda's Atlas Master Ascendancy specialises in powerful enemies and the loot that they drop, such as map bosses or even Pinnacle bosses. One option will cause Azmeri Wisps in your opened map areas to be unable to possess Rare enemies, meaning they'll only be able to possess any Unique enemies such as the map boss or any Rogue Exiles, increasing their difficulty and rewards.

Will of the Draiocht, Hilda's Huntsmanship third row option
Hilda's most powerful node option however is arguably one that will limit you to a single portal entry for Pinnacle bosses, but guarantee that you'll receive 2 exclusive boss-drop Unique items if you're able to overcome the challenge.
Doryani's Science is more of a jack-of-all-trades Atlas Ascendancy, with some options to improve the strength of your character, and others to increase difficulty or loot.
For example you'll be able to benefit from an additional opened portal to an area which may be useful if there are some particularly dangerous enemies, or if you simply cannot afford to lose out on the loot that could be obtained from that zone. Meanwhile, Doryani also offers an option that increases the Rarity of items dropped by Magic Monsters by 100%, allowing you to influence areas for more Magic packs to increases your chances of better loot drops.