You folks want to hear about an awesome Greek mythological lady? Then let me tell you about Amphitrite, Greek goddess of the ocean and secret boss of all things watery and tidal.
Amphitrite is, in popular Greek mythology, usually famous as the wife of Poseidon and co-ruler of the seas. Hesiod and Apollodorus call her a Nereid, one of the hundreds of sea-nymph daughters of the ancient water god Nereus and Doris, one of the daughters of Okeanos; other sources allude to her being more closely associated with Okeanos herself, suggesting that she might be an Okeanid in spite of not being explicitly identified as such. She is beautiful and closely associated with sea creatures, and in most classical Greek art appears alongside her husband, supporting him in his oceany endeavors.
It's easy to accidentally write Amphitrite off as less important than the other wives of the Greek cosmic kings, Hera and Persephone, who are extremely important and famous in their own right, because she doesn't have as many tales of her exploits as they do. But that would be a mistake, because while Amphitrite is not overtly powerful in the same way her counterparts are, she is secretly among the most important ladies ever to shake a fin-fringed leg in the depths of the Mediterranean.
Amphitrite's roots in Greek mythology are very ancient; archaeological evidence of her cults is among the oldest available, and in her earliest form she appeared not as a nymph or a family member of a more important deity but as a personification of the sea itself, which was thought of as essentially female in its unplumbable depths and mysterious ability to produce living things out of its waves, much like an archetypal womb. Sea monsters in Greek mythology are described as coming from the "breeding grounds of Amphitrite", suggesting her as the mother of powerful and dangerous creatures; the sea itself is referred to as belonging to her frequently in ancient poetry, from the waves being described as "Amphitrite's billows" to the entire ocean being called the "fish-wreathed bosom of Amphitrite". She is given titles such as the Sea Queen and frequently called "the moaner" or "loud-moaning goddess", which refers to the sound of the wind and waves on the open sea, and all fish and other sea creatures are called her children and considered under her control.
Her association with Poseidon makes sense, of course: she's a sea goddess and he's the king of the seas. But in a more ancient time when Poseidon's cult was rising to prominence and worship of the Olympians was overtaking that of the older, more elemental Titans and primordial deities, his marriage to Amphitrite wasn't just a convenient confluence of symbols, but a religious necessity. If Poseidon was to become the ruler of the seas, he must be seen to assert power over it in a concrete way; since Amphitrite is the sea, Poseidon marrying her meant establishing himself as the head of the household and gaining control over the sea and everything in it, the same way a mortal man marrying a woman in ancient Greece would gain control of any property she happened to own or create. It's especially noteworthy that where Hades and Zeus don't really have to grapple for control of the realms they are assigned in the drawing of lots, the ancient cult of the sea goddess requires Poseidon to find a way to legitimize himself when it comes to lordship over the waters.
The tale of Poseidon wooing Amphitrite is therefore a story not just of a god trying to convince a beautiful goddess to take him as her husband, but also the symbolic tale of how Poseidon came to be the lord of the seas in the first place. In it, Poseidon attempts to romance Amphitrite, but she refuses his overtures (according to Hyginus, because she wanted to remain forever a maiden, possibly in reference to the idea of the sea as a primordially female domain) and flees him, hiding herself in the ocean that his her domain so that he has no hope of finding her. Poseidon despairs, knowing that he can't compete with her abilities in the waters, and only successfully gains her hand later when a dolphin, likewise a creature of the sea and one of Amphitrite's many children, finds her and convinces her that she should accept Poseidon's overtures. She eventually agrees and returns to become his wife, and Poseidon places the creature in the sky as the constellation Delphinus as thanks for its help.
Later retellings of the story slowly begin to strip Amphitrite of her importance in it; Oppian claims that the dolphin merely told Poseidon where she was hiding so that he could kidnap her and marry her against her will, therefore allowing Poseidon to become the character with the power in the story and solidify the idea of him conquering the sea rather than negotiating his place in it, while Virgil goes full-on Roman and takes Amphitrite out of the equation entirely, implying that Amphitrite's parents intentionally "bought" Poseidon as a husband for their daughter with the dowry of the bountiful seas, therefore making her the supplicant who sought a powerful husband. But the further back you go, the more of those layers of later dude-centricism fall away, and the more clear it becomes that in the earliest Greek religious stories and cults, Poseidon needed to seek the blessing of the ladies of the ocean, not the other way around.
Amphitrite is not the only archaic sea-goddess to be considered incredibly elemental and important to the waters of the world; because of the ancient Greek idea of the sea as being in some way essentially female, the vast majority of the deities associated with it are women. The ancient Titanid Tethys is the first mother of the sea deities and the nurse to the Olympians besides, while ancient Thalassa was also a personification of the sea and the de facto mother of Amphitrite when Ouranos' semen fell upon her, Leukothea was the goddess of safe journeys on the ocean who defied Poseidon's attempts to destroy Odysseus and protected him on his way, and the numbers of the Okeanids and Nereids, female spirits of the sea, are almost uncountable (and include among their ranks other notable water goddesses, including Achilles' mother Thetis and the lovelorn Galatea). While there are male gods of the ocean - Okeanos, most obviously, along with other ancient primordial gods Pontus and Nereus - they are almost always passive and uninvolved in stories, while the female powers of the sea are the ones who wield power and decide between life and death.
Amphitrite's position as an adjunct to Poseidon is a sort of weird attempt at reversing ancient ideas of female power in the ocean to fit newer Greek models of powerful male leaders, and the result is that Poseidon becomes the preeminent sea-power of Greek mythology, but he can never quite shake the shadow of his extremely important wife, who is necessary to his continued power, or the fact that he's surrounded on all sides by ancient goddesses of wave and water.
In spite of her semi-erasure in later Greek myth, Amphitrite still has stories in which she acts on her own with decisive power over her domain, often so significantly that her powers echo across kingdoms. In the Argonautica, it is not Poseidon that the sailors of the Argo look for a sign from but Amphitrite, who an oracle tells them will send them a sign; she does so by unyoking one of Poseidon's horses and setting it to run free upon land, where the Argonauts see it and are able to follow it onward toward their goal. Amphitrite's ability to set Poseidon's horses free suggests not only that she can and does act without his blessing, but that she has as much power over his domain and possessions as he does, far from being a background character with no power over the sea after his arrival.
It is also Amphitrite who gives Theseus her wedding crown as a sign of his true divine heritage; again, it's interesting that although Theseus is the son of Poseidon (and not Amphitrite) and casts himself into the waves in order to prove that he can survive thanks to his father's favor, Amphitrite is the one who receives him, gives him the mark of legitimacy as part of the family of the sea, and sends him back unharmed to face his detractors. Poseidon's home is described as rich and beautiful, but Poseidon himself does not appear; the entire underwater portion of the myth is populated only by Amphitrite, the Nereids who accompany her, and the dolphins who are her children. Hyginus later adds that Thetis was also there, another woman of the briny deep, but also fails to mention Poseidon taking any direct action.
By the time of classical Greek religion's heyday, Poseidon was certainly the undisputed ruler of the Mediterranean, and Amphitrite reduced to a footnote as his wife and companion without any strong formal worship or stories of exceptional power. But her very existence is a call back to an earlier age when the sea was the domain of the untameable feminine, and just as she's managing to pull all our focus the painting above, she can never truly be completely overshadowed by her husband. She's always subtly at the core of power exerted over the waters, no matter who else lays claim to them in the meantime.