Actually Bill Gates BOUGHT DOS from a dentist who belonged to the same computer club that Gates did, and while IBM was going to offer him a hundred thousand dollars or so, Gates instead licensed it to them for $25/PC sold, which they thought was crazy as they only expected to sell a couple of hundred PC's per year. So in a way he 'stole' it in the sense the he retained ownership and IBM had to continue to pay him millions every year.
BTW, the original name of DOS was QDOS, which stood for 'Quick and Dirty Operating System' and for which Bill Gates paid $50,000 to his dentist friend, so that's who he really stole it from 
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