Why is Chromosome 1 called Chromosome 1?
Chromosomes were first known about from karyograms (that's the word for chromosome pictures like these) sort of like this one (1)(2):



The scientists looking at these chromosomes didn't know much about them at first. They were discovered before anything was understood about genes, but by 1922 it was thought they were the carriers of genes. Without much understanding of the chromosomes, and certainly no understanding of what they carried, scientists needed an easy way to order and compare them. They chose a straight forward option - size - and paired them up and then lined them up biggest to smallest. Because the sex chromosomes didn't fit into this scheme of matching pairs they were left to the end.

Hence Chromosome 1 is Chromosome 1 because it is the largest autosomal chromosome.

Notes:


The actual first karyogram was of a plant, this one is of a human male.
The image above is public domain, obtained from Wikipedia, and originally made by the National Human Genome Research Institute.