Question: Euthyphro of Prospalta, and Socrates are best know by the writings of who?

Context paragraphs:
Memorabilia (Xenophon): Memorabilia (original title in Greek: Ἀπομνημονεύματα, "Apomnemoneumata") is a collection of Socratic dialogues by Xenophon, a student of Socrates.  The lengthiest and most famous of Xenophon's Socratic writings, the "Memorabilia" is essentially an apologia (defense) of Socrates, differing from both Xenophon's "Apology of Socrates to the Jury" and Plato's "Apology" mainly in that the Apologies present Socrates as defending himself before the jury, whereas the former presents Xenophon's own defense of Socrates, offering edifying examples of Socrates' conversations and activities along with occasional commentary from Xenophon.

The Death of Socrates: The Death of Socrates (French: "La Mort de Socrate" ) is an oil on canvas painted by French painter Jacques-Louis David in 1787.  The painting focuses on a classical subject like many of his works from that decade, in this case the story of the execution of Socrates as told by Plato in his "Phaedo".  In this story, Socrates has been convicted of corrupting the youth of Athens and introducing strange gods, and has been sentenced to die by drinking poison hemlock.  Socrates uses his death as a final lesson for his pupils rather than fleeing when the opportunity arises, and faces it calmly.  The "Phaedo" depicts the death of Socrates and is also Plato's fourth and last dialogue to detail the philosopher's final days, which is also detailed in "Euthyphro", "Apology", and "Crito".

Socrates: Socrates ( ; Greek: Σωκράτης , "Sōkrátēs"; 470/469 – 399 BC) was a classical Greek (Athenian) philosopher credited as one of the founders of Western philosophy.  He is an enigmatic figure known chiefly through the accounts of classical writers, especially the writings of his students Plato and Xenophon and the plays of his contemporary Aristophanes.  Plato's dialogues are among the most comprehensive accounts of Socrates to survive from antiquity, though it is unclear the degree to which Socrates himself is "hidden behind his 'best disciple', Plato".

Phaedo: Phædo or Phaedo ( ; Greek: Φαίδων , "Phaidōn", ] ), also known to ancient readers as "On The Soul", is one of the best-known dialogues of Plato's middle period, along with the "Republic" and the "Symposium".  The "Phaedo", which depicts the death of Socrates, is also Plato's fourth and last dialogue to detail the philosopher's final days, following "Euthyphro", "Apology", and "Crito".

Euthyphro: Euthyphro ( ; Ancient Greek: Εὐθύφρων, "Euthuphrōn" ), [ca. 399–395 BC], by Plato, is a dialogue whose events occur in the weeks before the trial of Socrates (399 BC), for which Socrates and Euthyphro attempt to establish a definitive meaning for the word "piety" (holiness).

Euthyphro dilemma: The Euthyphro dilemma is found in Plato's dialogue "Euthyphro", in which Socrates asks Euthyphro, "Is the pious (τὸ ὅσιον) loved by the gods because it is pious, or is it pious because it is loved by the gods?"  (10a)

Grigor Magistros: Grigor Magistros (Armenian: Գրիգոր Մագիստրոս ; "Gregory the "magistros""; ca. 990–1058) was an Armenian prince, linguist, scholar and public functionary.  A layman of the princely Pahlavuni family that claimed descent from the dynasty established by St. Gregory the Illuminator, he was the son of the military commander Vasak Pahlavuni.  After the Byzantine Empire annexed the Kingdom of Ani, Gregory went on to serve as the governor ("doux") of the province of Edessa.  During his tenure he worked actively to suppress the Tondrakians, a breakaway Christian Armenian sect that the Armenian and Byzantine Churches both labeled heretics.  He studied both ecclesiastical and secular literature, Syriac as well as Greek.  He collected all Armenian manuscripts of scientific or philosophical value that were to be found, including the works of Anania Shirakatsi, and translations from Callimachus,  Andronicus of Rhodes and Olympiodorus.  He translated several works of Plato — "The Laws", the "Eulogy of Socrates", "Euthyphro", "Timaeus" and "Phaedo".  Many ecclesiastics of the period were his pupils.

Euthyphro (prophet): Euthyphro of Prospalta ( ; Ancient Greek: Εὐθύφρων Προσπάλτιος ; fl.  400 BCE) was an ancient Athenian religious prophet ("mantis") best known for his role in his eponymous dialogue written by the philosopher Plato.  The debate between Euthyphro and Socrates therein influenced generations of theologians and gave rise to the question of the relationship between God and morality known as the Euthyphro dilemma.

I know that I know nothing: The phrase "I know that I know nothing" or "I know one thing; that I know nothing", sometimes called the Socratic paradox, is a well-known saying that is derived from Plato's account of the Greek philosopher Socrates.  The phrase is not one that Socrates himself is ever recorded as saying.

Ideal (group): Ideal was an American R&B quartet from Houston, Texas, United States.  The group Ideal debuted in 1999 and is composed of brothers Maverick Cotton and Swab, their cousin PZ and high school friend J-Dante.  The group is best known for its hit songs "Get Gone" and "Whatever."  Ideal also had a 5th member who started with the Original Group in 1992, Charles Vienn II, who now goes by the stage name "EDWIN VICTORY".  He left the group in 1998 to pursue his own musical and entertainment interest.  He is best know for his creation of "The Baby Isaac Crew", a group of mascot characters who do positive and uplifting hip hop songs for kids.

Supporting paragraphs: Euthyphro (prophet) Socrates
Answer: Plato