Alexander (or Aleksander) is the old man who saved the Star League before fucking off and leaving it to the mercy of the Great Houses, his fuck-up of a son who created the Clans is Nicholas Kerensky, and his other son who should have been the one who lived was named Andery Kerensky.
Naturally the Clans all fellate Nicholas, pay some lip service to Alexander for getting them out of the Inner Sphere, and completely forget that Andery ever existed, despite the fact that the 99% of the Kerensky genes still floating around are probably his on account of the fact Nicholas was quite literally insane as a result of inherited mental issues on his mother's side of the family that Andery seems to have thankfully avoided.