The left is a Person (see Post 37), the right is its another person but facing to right, opposite direction.
The original meaning of this character is Opposite.
The big seal script for the character is
The small seal script for the character is
The clerical script for the character is
When was the meaning changed from Opposite to North? I don't know, but it was very early, at least 2000+ ago.
How was this North from?
In Chinese history, almost all palaces for Kings or Emperors face south, and Kings or Emperors sit facing to south. Opposite is comparison with Palace or King/Emperor facing, which is North.
The pinyin for the character is Bei3.
Now we have learnt three characters which have two characters of Person: 北，从，比。It is interesting to compare them.
Shell bone script
From left to right: Follow (从), Compete (比), North (北）
Two people face left is Follow (See Post 74), two people facing right with two forearms up is Compete (See Post 162), two people standing back to back, facing opposite directions is North.
Small seal script