What we know of Handel’s personality comes from surviving letters, quotes, and anecdotes. His most striking physical feature was his corpulence, and he purportedly enjoyed food and drink immensely. This gave rise to satires such as the cartoon below by a contemporary, which depicts him as a gluttonous hog at the organ. However, this appetite was balanced by a generous disposition. He gave much to charities and friends, and those who knew him spoke highly of these qualities. At his death he gave a considerable portion of his fortune to London's Foundling Hospital orphanage, and helped establish a charity to support musicians and their families during hard times, which still exists in England today as the Royal Society of Musicians.
Though he had many friends and acquaintances, Handel was inclined to be private about his personal affairs. Not only did he never marry, but there is scant evidence to indicate any romantic attachments. And due to his reluctance to cooperate with biographers later in life, several aspects of his life are not as well documented as we might like.
In his traveling he picked up many languages, but always spoke with a clear German accent. His languages tended to run together, particularly when he got angry or flustered. He could be quite temperamental, and a few stories have him throwing tantrums. (For an example, he once picked up a soprano and threatened to throw her out of a window.) But those who knew him stated that he was never the type who held a grudge, nor any real malice toward anyone. He seems merely to have been particular about his art, and a bit irascible when crossed. Though his outward behavior could seem abrasive, and often amusingly so, inside he was more gentle than most, and free from ill-will.
Handel’s religion has been a source of interest. Though by all accounts he was quite devout and believed strongly in charity, his particular denomination remains a mystery, if he followed one at all. Some characterize him as a humanist, very tolerant and accepting of all faiths. Most of his music was for the theater instead of the church, and human drama and the experience of this world were what captured his interest.
Compared with most composers, Handel was notable for his independence and industry. He never accepted a court appointment, church position, or any official patron. Though opera and oratorio were uncertain ventures, drama was what he wished to create, and this necessitated constant work and entrepreneurship. As great an artist as he was, he seems to have realized that fulfilling his goals would require more than just writing music, and he never shied away from other responsibilities. Despite many obstacles and setbacks, his humility and hard work paid off in the end, and he was one of the few composers of his day to end his life in prosperity and good standing in his community. And in addition to securing his own place, he shared his success with others and raised the fortunes of those around him.
One of Handel's friends put it best when he said of him: "He died as he lived - a good Christian, with true sense of his duty to God and man, and in perfect charity with all the world."
For more information about Handel's life there are many published biographies available. I have not read all of them, so I cannot recommend the best. My advice would be to decide how much information you want and then find one that seems roughly the right thickness. Some of the pages in our Links section also have additional info, and gfhandel.org has very helpful chronologies of his life and major works.
Biography: Upbringing and Early Career | Handel's Opera Career | Transition to Oratorios | Final years | Legacy | Personality