Is it possible to train yourself to need less sleep?

I know it depends on the person. For me, I find that 8h to 9h of sleep per night give me enough rest. I can usually do ok with 7h. But drop my night to 6h, and I become a zombie for the rest of the day. It’s always been like this.

And then there’s my friend, who can sleep 4 or 5h and be fresh and ready to go in the morning, with enough energy for the entire day. Needless to say, it’s something that comes in handy for him during busy weeks. How does he do it (if he does anything)? And can I train myself to sleep less without damaging my health?