In the Biblical parable of the Prodigal Son, a son receives his inheritance and travels to a distant country, wastes all his money in wild extravagance, becomes desperately poor, returns to his father, and is received with open arms. Prodigal, here and elsewhere, means rashly or wastefully extravagant.
But in modern use, the phrase prodigal son has strayed from its Biblical associations. It usually focuses on aspects of the parable involving the son’s wandering and eventual return, and it ignores the part about extravagance and wasteful spending.
In the following examples, the so-called prodigal son has been away and now returns, but there’s no suggestion that he has been extravagantly wasteful. In fact, if you view the articles the examples come from, you’ll see all three refer to men who went off and became successful through hard work and dedication (the opposite of prodigality):
That changed once prodigal son Willie Taggart returned from Stanford to take over his alma mater. [News Enterprise]
The largest corporate prodigal son in the history of technology stocks has taken a leave of absence from his role as CEO of Apple. [Hawke's Bay Today]
He became Brooklyn’s prodigal son to the outside world, as he often made reference on his albums and on-stage to his love of Bed-Stuy and of Brooklyn. [Patch]
This questionable use of prodigal son is common, so it must be accepted as a secondary definition.
Still, some writers use the phrase with the sense of prodigal intact—for example:
Lee Tamahori’s Uday Hussein biopic showcases the prodigal son of the world’s most evil clan as a sort of oversexed/overdrugged/bi-polar and over-the-top Tony Montana for the post-post war video game age. [Salt Lake Magazine]
Godard was the prodigal son of a bourgeois Swiss family whose favourite scam had been to purloin his grandfather’s antique books to make some pocket money; at the time, he was considered a liability. [Financial Times]