Burt Hudson is Cora Hudson's deceased husband, and Mindy's maternal grandfather.
About Burt Hudson[]
Though never directly named in screened scenes, Cora names her husband as 'Burt' in a trimmed scene in Season 1's Mork's Mixed Emotions that remains in full in the Shooting Script.
As per Cora's reminiscences, Burt and she met very young, though it took them 15 years to realize it had been love at first sight. (Mork in Love).
After marrying, they had Elizabeth, Mindy's mother, and at least one other daughter, who would go on to be the mother of Nelson and his sister (as Nelson must be a maternal cousin, due to Fred only having one sibling, brother Dave, and Nelson not being a McConnell).
It is not known when precisely Burt passed away but as Cora states they were married for over 40 years (Mork's Mixed Emotions script) it is likely to have been a few years after the death of daughter Elizabeth, which occurred when Mindy was still only 6 years of age.