Strongmaster

The seven second-most-powerful people in all of the Dune sea

With a sigh, the honorable High Prince Hadar set his reed pen aside and examined the paper he had almost ruined. Another rumbling bang shook his room and he hastily grabbed the ink pot before it could spill over his desk. As he rose another shock, this one strong enough to send him stumbling, shook the building. He opened his chambers door.
"Iram, go find my brother for me", spoke the heir to the great oasis Elazzar to his steward, "and tell him to break rocks somewhere else but exactly beneath my quarters. I doubt our father would appreciate to pay for yet another set of carpets ruined by ink."

The title of Strongmaster is directly and irreplacably tied to wielding one of The Hammers of Jadira, and is therefore also tied to the risks of the position.
Strongmasters are appointed for life by the lord of the major oasis, who is also the owner of the Stronghammer. Usually the position is granted to second sons, brothers or if none of the above can be determined relatives of important allied families. Because of the strictly gendered society that governs Jadira women are never chosen for the position and because of political risks, the chosen person is always one directly from the oasis.

Cycles of Strongmasters -- or How to become a Strongmaster

Jadiran folly (via Midjourney) by Ninodonlord

If possible, the former Strongmaster, supported by specifically tutored and educated aides, is tasked with training the next Strongmaster, who is usually in his teens at the time of appointment. If the previous Strongmaster died in battle, the aides take the place of primary educators instead.
The new pupil must first undergo a rigorous training of strength and agility, for the Stronghammers only improve the capabilities that are already there. The stronger the master, the more powerful their wielding becomes. Once they are deemed ready by their tutors, the new Strongmaster starts drilling basic attacking movements and patterns with regular hammers that already are heavier than regular Warhammers.
Then they are taught the rituals of awakening their hammer first in theory, while also learning basic thaumaturgic and medicinal theory, so that they can make the safe and healthy decisions in cases of emergency, should they be separated from their retinue.
Then, at last the Strongmaster is taught the use of their hammer, at which point they are officially the new Strongmaster of their Oasis. Practice still does not usually use the Hammer itself, because of the immense toll on the body (more on that later).

Role in War

The Strongmaster essentially functions as a walking siege weapon under the command of the High Lord they are sworn to. When an enemy fortification needs to be taken, the Strongmaster is brought to the walls either using subterfuge or by forcing a covered approach in battle. If he can reach the walls, his Stronghammer can bring down walls and gates with terrifying ease.
Because of this ability, the High Lords of the seven oases rule supreme and can exert far more control of other settlements within their borders than otherwise possible. Strongmasters are also used as deterring agent in conflicts. The threat of a Strongmasters power is often used in negotiations and may be just the bargaining chip the High Lords needs to get what he wants.

Privileges and Luxuries

Because of this and other reasons that will become apparent in the next section, Strongmasters enjoy a great deal of support and advantages in their oasis. They are exempt from all but the religious taxes by law (though most of the time they would be part of the royal family and as such already be paying into their own coffers), and are paid a handsome monthly reward, usually even higher than the commanding generals of the oasis' army. They have the right to purchase any Sahal from any Jadiran, though it is expected that they offer a fair price for the steed. Finally, they can expect to receive a holding and reign over a smaller nearby oasis when (or if) they retire from their position.
On a more abstract level, Strongmasters have one of the highest standings in Jadiran society. Their position is seen as highly lucrative and as a result they can expect far more favorable matches for marriages than they would receive otherwise. Additionally, they are often surrounded by a sizable retinue who are either on their direct payroll or hoping to use the good graces of the Strongmaster to further their own goals. This is because Strongmasters usually have a very good relationship with the local lord and may be able to exert influence on that lords decisions.

Risks and Tolls

All of the above can partially be explained by the inherent value of the Stronghammers. However the handsome pay and societal advantages were also implemented, because the position is one of severe risk of death in wartime and because of the damage it does to the body.
The risks during wartime stem from the role the Strongmaster fills in a High Lords army. They are often part of the vanguard when attacking a fortified position and the danger they pose to the defenders further places a target on their metaphorical back. Even though the High Lord will try to protect his investment in the Strongmaster as much as he can, the risk of dying in a siege is still significantly higher than any other part of the army.
Additionally, despite the protective magic leaking from the Stronghammers, wielding one places enormous strain on the limbs and joints of the Strongmasters body. They simply cannot take unlimited impacts of their weapon and as such, after 20 years or earlier depending on the intensity of using the Strongmaster, the wielders body is so destroyed that they need to retire. Signs of these physical tolls include significant damage to tendons and deterioration or even loss of cartilage in the joints as well as broken musculature.

Retirement

If a Strongmaster survives their time as one and it becomes apparent his retirement is imminent, he is tasked with training the next holder of the title. This earns him the title of Strongmentor. Once the next Strongmaster finally takes over, he is called Strongsage and is free to pursue any retirement he sees fit. He however is still required to remain as part of the same oasis as his birth, because of the intimate knowledge he still posesses of the Stronghammer and its secrets.