Ք is the first letter of the Armenian translation of the Gospel of Luke. As it is known, the symbol of the Evangelist Luke wais the bull, therefore, in handwritten medieval Armenian Gospels letter Ք was often depicted as a bull. There are two principal versions regarding the origin of the graphic form of letter Ք. Supporters of the first version are of the opinion that Ք was derived from the Greek X (chi), and it should be mentioned that although the modern versions of these letters are not similar, among the earliest examples of Greek X there are actually some that resemble our Ք. German paleographer Victor Gardtgauzen was of another opinion: he believed that the Armenian Ք was derived from one of the varieties of the monographic cross, or the Christogram.
This type of cross, widespread in the IV–V centuries, was a monogram of the Greek letters P (rho) and T (tau), which symbolized the Heavenly King (Latin: Rex – the king) and the Tshaped cross on which He was crucified. It is possible, however, that Ք could be formed by rotating another variety of the Christogram – , composed of the Greek letters X and P – the first letters of the name of Christ. Armenian linguist Hrachya Acharyan does not agree with Gardtgauzen’s hypothesis, believing that “our pious Armenians would not allow themselves to play with such holy names.” But we must not forget that what may seem to us to be a game, was an attempt at a symbolic reflection of the world for the early Christians. There are numerous examples evidencing this not only in Armenian, but also in alphabets of other Christian nations. Thus, the first letter of the Slavonic Glagolitic alphabet has the shape of the cross ( ), and in the ancient Georgian alphabet the first letter of the Georgian form of the name “Christ” is a quadrangular cross – [kh]. Just like the Georgian , Armenian Ք is the first letter of the name Քրիստոս ([Qristos] – Christ). It is believed that Mashtots put it at the end of the alphabet, so that together with the first letter Ա – the first in the word Աստված ([Astvats] – God) and the symbol of God the Father, it could convey the symbolism of the New Testament revelation of Christ: “I am the Alpha and the Omega, the beginning and end.”
See more at Aram Khachaturians "Armenian Alphabet. History and Symbolism" book