As a young man he wished to marry Mrs. Everdeen, who instead chose her husband because of his beautiful singing voice. Their daughter, Katniss Everdeen, often traded with Mr. Mellark. When she was about to leave to the Capitol for the 74th Hunger Games, Mr. Mellark came in to say goodbye to her. He gave Katniss cookies, that she later threw away, and promised her that he would feed Katniss' sister in her absence.
It was believed that he and the rest of Peeta's family were killed when District 12 was firebombed.
Mr. Mellark is the father of three sons, including Peeta, and is the husband of Mrs. Mellark, who is known throughout District 12 as a "witch".
As Katniss decribes him, Mr. Mellark is a broad-shouldered man with burn scars from years at the oven. The book does not say anything about his height or weight.
Though not much is said in the book about his personality, he seems kind-hearted, repectful, maybe a little bit a pushover as he lets his wife do whatever. He might also still be upset that he never got to marry Mrs. Everdeen, however he takes care of her children (he promises Katniss he won't let Prim starve and always buys Katniss's squirrels although his wife would never approve).