Hipparchus (son of Peisistratos) in Wikipedia
Hipparchus or Hipparch (Ἵππαρχος) (d. 514 BCE) was a ruler of Athens. He was one of the sons of Peisistratos.
Although he was said among Greeks to have been the tyrant of Athens along with his brother Hippias when Pisistratus died, about 527 BC, in actuality, according to Thucydides, Hippias was the tyrant. Hipparchus was a patron of the arts; and it was Hipparchus who invited Simonides of Ceos to Athens.
In 514 BC Hipparchus was murdered by the Tyrannicides, Harmodius and Aristogeiton. This was apparently a personal dispute, according to Herodotus and Thucydides. Hipparchus had fallen in love with Harmodius, who was already the lover of Aristogeiton. When Harmodius rejected him, Hipparchus invited Harmodius's sister to participate in the Panathenaic Festival as kanephoros only to spurn her when she appeared in her finest, insinuating that she was not a virgin. As a result, Harmodius and Aristogeiton assassinated him.
After the assassination, Hippias became a bitter and cruel tyrant, and was overthrown a few years later in 510 by the Spartan king Cleomenes. Modern scholarship generally ascribes the tradition that Hipparchus was a tyrant himself - as opposed to having a privileged position as the tyrant's brother - to the cult of Harmodius and Aristogeiton established after the revolution.
Hipparchus in Harpers Dictionary of Classical Antiquities
A son of Pisistratus. (See Pisistratidae.)
A Greek mathematician, the founder of scientific astronomy. He was born at Nicaea in Bithynia about B.C. 160, lived chiefly at Rhodes and Alexandria, and died about B.C. 120. He discovered the precession of the equinoxes, settled more accurately the length of the solar year, as also of the revolution of the moon, and the magnitude and distances of the heavenly bodies. He placed mathematical geography on a firmer basis, by teaching the application of the latitude and longitude of the stars to marking the position of places on the surface of the earth. He is also regarded as having invented trigonometry. In plane trigonometry he constructed a table of chords of arcs, which is practically the same as one of natural sines; and in spherical trigonometry he had some methods of solving triangles. Of his numerous writings we possess only his commentary on the Phaenomena of Eudoxus and Aratus and a catalogue of 1026 fixed stars. The famous Almagest of Ptolemy (Μεγίστη Σύνταξις) is founded on the writings of Hipparchus. See Ball, Short Hist. of Mathematics, pp. 79-81, 90 (London, 1888).