Greek chi, through Etruscan from the Western Greek alphabet.
X
the Greek alphabet had two regional forms, and they disagreed about this letter: in the Western (Euboean) form X already meant [ks], in the Eastern (Ionic) form it meant a rough [kh]. Latin took the Western value through Etruscan; the Cyrillic Х took the Eastern one. Same drawing, two jobs, and the split happened inside Greek itself.
In the modern alphabet this letter is number 24 of 26. Before it comes W, after it Y. The order itself is inherited: Latin took it from Greek, Greek from Phoenician, and the sequence has survived largely unchanged for about three thousand years. Every rearrangement since has been an insertion, not a reshuffle.
This is a consonant: it sets the hardness of a name and how it meets the next word. In a corpus of 315 surnames none begins with it; 2 end on it. Among the 96 given names in the base it appears in 1. One occurrence per surname is the ceiling: no surname in the corpus repeats this letter.
Alexander
These letters came from the Greek alphabet.