It may be a solar keratosis, a precancerous sunspot. However, it may also be a basal cell carcinoma or a squamous cell carcinoma. While these are not as serious as melanomas, they do need to be treated. So what you need to do is have your father see a dermatologist, who can perform a biopsy and treat as needed. Since this has been there for 1-2 years, I'd do this sooner rather than later.
Best.
Dr. Rockoff