uk – Can my friend from the U.S visit the U.K. after a custodial sentence

My friend in the U.S was sentenced to 1 year and a day, he actually served just 8 months, that was ten years ago, the crime was financial, he only wants to visit for about ten days, meet with friends he is 78, was refused 5 years ago after enquiring, I can stand guarantor for him what’s the ruling .. many thanks in advance.