Title says it all.
For my own part; I am looking to learn and adopt a play style which does not necessarily win, but is typified as being incredibly difficult to actually win against.
World Champion Tigran Petrosian was known to be almost impossible to beat. He's your man. Study his games and legacy.
Per Wikipedia, he lost 1 out of 129 Olympiad games. Olympiads are top-notch tournaments and the score is over 20 years of play. He's not a flash in the pan.
In his 8 Euroteams competitions (held every three years from 1957 to 1983) he lost -0- out of 52 games. His team won the competition every time.
Then I started poking around in chessgames.com and I started looking at win/loss/draw ratios.
I made a list of all world champions since Botvinnik, including the weird ones where FIDE lost control.
The three players with the best win:loss ratio (in order): Kasparov (6.62), Fischer (4.87), and Petrosian (4.38). Kasparov dominates. (Only Karpov and Botvinnik are in the same class as these three.) I expected Kasparov and Fischer to be in this list. I was surprised that Petrosian was there, to be honest. But we see that he was very much able to score the win. He's about like Fischer in this regard.
The three players with the best win:draw ratio, in order: Fischer (1.7), Botvinnik (1.22), and Kasparov (1.02). Fischer dominates. No other players are in their class. I attribute this to an uncompromising aggressive desire to win. No half measures. Petrosian was not afflicted with this mentality. If it did not fit, he did not force it.
The three players with the best draw:loss ratio, in order: Petrosian (6.74), Kasparov (6.52), and Kramnik (6.25). Spassky and Karpov trail. No one else is close. This means that even if you had an advantage over one of these players, you'd have to work like mad to score the full point.
The three players with the best win+draw:loss ratio, in order: Kasparov (13.14), Petrosian (11.13), and Kramnik (9.73). Each is dominant over the next. Karpov and Spassky follow Kramnik closely. This reflects upon the difficulty of scoring the full point. An opponent would twice as likely to nick a full point off Carlsen than Petrosian. Ouch. (I think this is a statistical fluke due to Carslen's age...but it makes a good story.)
Finally, while I did not list it, Petrosian has one of the lower win:draw ratios. He was more than willing to accept a draw if he could not see how to secure the win. Other players with a similar win:draw ratio do not possess Petrosian's compensating win:loss ratio, however.
This rather defines his style, I think. You can see here a player who will defeat you if you aren't careful. He is patient and takes few chances. If you get ahead of him, he'll likely wear you down, into a draw. And if you err, he'll crush you.
edit - fun facts for the world champions...
In the 4 ratios I looked at (w:l, w:d, d:l, and w+d:l)...
My guess would be Ulf Andersson.