Here is how Christopher Parker Pyne was first described in The Case Of The Middle-Aged Wife:
"Somehow or other, the very appearance of Mr Parker Pyne brought a feeling of reassurance. He was large but not to say fat; he had a bald head of noble proportions, strong glasses, and a little twinkle in his eye."
Parker Pyne is a retired government employee turned philanthropist who considers himself to be a "detective of the heart." The exact nature of his former job and his former position in the British government was never stated but he claimed to have been involved in the gathering of statistics. This leads to the theory that his job was the same as Mycroft Holmes, a human super computer, specialising in omniscience.
This theory carries some weight as the resemblance between Parker Pyne and Mycroft Holmes is hard to deny. Both are heavy set fellows. Both appear to possess superior skills to that of their counterparts (Sherlock Holmes/Hercule Poirot) but they are both nonetheless incapable of performing similar detective work since they are both unwilling to put in the physical effort necessary to bring cases to their conclusions.
While he does occasionally exert himself in the stories where he is on vacation, he on the whole remains a sedentary problem-solver, providing solutions based on seemingly little evidence and trusting his agents to handle any of the practical details. He himself rarely goes to see his clients after their first meeting, although he get reports on their progress from his hench-people. In fact, Pyne's own lack of drive and faith in his minions' skills can be a severe handicap despite his deductive talents, as it resulted in the failure of his efforts in "The Case Of The Discontented Husband", Pyne's only recorded failure.
Parker Pyne is also an uncommon type of detective, who doesn't usually investigate murders or similar crimes, but rather prefers to help his clients to reencounter happiness. For such, he applies the knowledge he has acquired in 35 years of work in a statistics office, from which he retired, establishing later on his own on 17 Richmond Street, London.
He has a theory that there are five main types of unhappiness and all are logically resoluble. His methods are unorthodox and he often employs deception and constructs elaborate charades to fool the suspects and cure unhappiness successfully.
Though he is, apparently, limited to a specific type of investigation, Pyne also has uncommon capabilities for criminal investigation. He works alongside his neurotic assistant Miss Lemon, novelist Ariadne Oliver, handsome lounge lizard Claude Luttrell and disguise artist Madeline de Sara. Whatever the case is, he always has the aid of his team (outnumbered, but as effective as they are extravagant).