'Investment banker' is used as a broad-brush term to cover a large number of different job functions. True investment bankers have a very different job to salespeople/traders.
Salaries for juniors (associates) on the true investment banking side are still very high, but probably not as high as you would think. They are also likely to be working 100+ hours a week.
Base salaries take a jump once they reach the grade of vice president / director. Managing directors will be on the mega salaries.
Having said that, quantative traders of all grades earn high base salaries. These folks work out the mathematical calculations for complex financial instruments. Requires a minimum 2:1 maths/physics degree from a good university, plus a relevant internship. I knew one who had previously been a rocket scientist.
All salaries will have a base element plus a performance related element ('bonus', paid annually). Bonuses are paid as part cash, part shares. In most places you can't touch/sell the shares for a set period after they have been awarded. If you leave the firm within 6 months of being given a bonus, you have to pay it back. It's longer for conduct related matters, e.g. if a person is sacked becaused they breached rules, bonuses (most likely shares) from the previous 5 years can be taken back.
If the person you know is a true investment banker (rather than one of a number of different roles in an investment bank), I'm sure they will have a private investment portfolio and will be paying vast sums into their pension.