Johnson Johnson is an agent for British Intelligence.
According to a brief in the front of the book "Dolly and the Bird of Paradise" (also known as "Tropical Island"), the man with the same first and last name is a "portrait painter, yachtsman, and unpaid official investigator".
His boss is Sir Bernard Emerson who runs an agency that is part of the British Secret Service. As the series begins, Johnson has just finished recovering from a mysterious explosion which nearly killed him and did take the life of his wife. It took a strange and interesting case to get him out of his depression but once that happened, his new life began.
That life consisted of painting much sought after portraits for the rich and famous. Johnson travels to most of the locations for his artistry onboard his much prised yacht, christened the "Dolly". His bohemian lifestyle now seems to suit him with his unruly hair, unkept clothes, and a seemingly souciant attitude. The most distinguishing aspect to him, one that is mentioned almost immediately by each main character in the books, are his bifocals. Described as "housefly" in one book, they must be remarkable though exactly why is not stated.
Each book in the series concerns a different character. The person is usually quite independent and capable of taking care of herself under normal conditions but then is thrown into situations which are far from ordinary. Just as circumstances seem about to become too much, in walks Johnson to put a bit of calmness and normalcy to life.
Even though these are undoubtedly firmly in the romance category, there are no great love affairs between the heroine of each book and Johnson. Most have already someone they care for or meet someone during the adventure. Johnson is just there to help and then to sail off at the end to another mystery.