Fixed star:  AGENA  Hadar
Constellation:  Beta (β) Centaurus
Longitude 1900:  22SCO24 Longitude 2000:  23SCO48
Declination 1900:  -59.53' Declination 2000:  -60.22'
Right ascension:  14h 03m Latitude:  -44.08'
Spectral class:  B3 Magnitude:  0.61 Variable

The history of the star: Agena

from p.154 of Star Names, Richard Hinckley Allen, 1889.
[A scanned copy can be viewed on this webpage]

Agena

Beta (β) Centaurus, Agena, the 10th brightest star in the sky, is located on the left front knee of the Centaur.

Burritt's Atlas of 1856 located this near the right fore leg, calling it Agena, but gave no meaning or derivation of the word, and I have not found it elsewhere; the 17th century German astronomer Bayer placed it on the left hind quarter ["Allen, who correctly deciphered the meaning of Bungula (p.152) for alpha (α Toliman), failed to recognize Agena as a similar compound, a and gena, the knee", Greek alpha and Latin gena, "the knee" marking the knee of the centaur's left front leg — Donald H. Menzel, 1963].

Hadar and Wazn, Ground and Weight [Hadar is said to mean "The settled land"; "as opposed to the desert"], seem to have been applied without much definiteness to alpha (α Toliman) and beta (β Agena) of this constellation, and to stars in Argo Navis, Columba, and Canis Major, probably on account of their proximity to the horizon; the meridian altitude of beta (β Agena), 1000 years ago at Cairo, in 30° of north latitude, being only 4°. The 17th century English orientalist Thomas Hyde, however, said that alpha (α Toliman) and gamma (γ) were the stars referred to by these Arabic titles.

The Chinese call beta (β Agena) Mah Fuh, the Horse's Belly.

This star beta (β Agena) and alpha (α Toliman) are the Southern Pointers, i.e. towards the Southern Cross (Crux), often regarded as the Cynosure of the southern hemisphere [the northern cynosure, or center of attention, is Polaris or Ursa Minor].

The Bushmen of South Africa knew them as Two Men that once were Lions; and the Australian natives as Two Brothers who speared Tchingal to death, the eastern stars of the Cross (Crux) being the spear points that pierced his body.

[Star Names, Their Lore and Meaning, Richard Hinckley Allen, 1889]. 

The astrological influences of the constellation Centaurus

According to Ptolemy the stars in the human part of the figure are of the nature of Venus and Mercury, and the bright stars in the horse's part of Venus and Jupiter. It is said to give hard-heartedness, inclination to vengeance, love of arms, strong passion, and an energetic nature. It may be connected with poisons. [Robson*, p.37.]

The astrological influences of the constellation Centaurus given by Manilius:

"The Centaur, from his own nature assigns qualities to his progeny. Such a one will either urge on asses with the goad and yoke together quadrupeds of mixed stock or will ride aloft in a chariot; else he will saddle horses with a fighter or drive them into the fight [translator's note; he will load horses with arms or drive them into arms, that is yoked to war-chariots].  

"Another knows how to apply the arts of healing to the limbs of animals [translator's note; these endowments reflect the identification of Centaurus as Chiron] and to relieve the dumb creatures of the disorders they cannot describe for his hearing.

"His is indeed a calling of skill, not to wait for the cries of pain, but recognize betimes a sick body not yet conscious of its sickness". [Astronomica, Manilius, 1st century A.D, book 5, p.329]. 

The astrological influences of the star Agena

According to Ptolemy it is of the nature of Venus and Jupiter, but Alvidas suggests an influence similar to that of Mars conjunction Mercury. It gives position, friendship, refinement, morality, health and honor. [Robson*, p.117.]

If this fixed star is in connection with Mercury or on the Ascendant and in conjunction with a "benefic", it can be taken as a promise for happiness and success. Tied up with Venus however, this star will make for pronounced sensuality; if, in addition to this, it is tied up with Mars, Saturn or Neptune, then the native may be subject of gossip or scandal. [Fixed Stars and Their Interpretation, Elsbeth Ebertin, 1928, p.68.]

A significator of success. [Larousse Encyclopedia of astrology].

With Sun: Mental activity, rashness, success, many friendships. [Robson*, p.118.]

With Moon: Sarcasm and bitter speech, strong passions. [Robson*, p.118.]

With Mercury: Great mental ability, sarcasm, material gain, speaking, writing and championing the masses. [Robson*, p.118.]

With Venus: Poetical, strong passions, rash friendships with women. [Robson*, p.118.]

With Mars: Legal authority, honor as speaker or writer, great mental and physical powers. [Robson*, p.118.]

With Jupiter: Intellectual success, legal and Church authority, professional honor. [Robson*, p.118.]

With Saturn: Thoughtful, shrewd, association with medical men, healing powers, abrupt manner, occultism, domestic disharmony through jealousy. [Robson*, p.118.]

With Uranus: Sarcasm, public work but eventual disfavor of superiors, caustic speaker and writer, violent, coarse, unrefined, strong passions, domestic disharmony, loss of expected wealth, peculiar death. [Robson*, p.118.]

With Neptune: Sharp, rash, headstrong, original, organizer, poor executive ability, loss through law and speculation, obstacles to success, many false friends and enemies, liable to accidents, death by colds or fevers. [Robson*, p.118.]

References:

*[Fixed Stars and Constellations in Astrology, Vivian E. Robson, 1923].