David is a friend of Brian. He speaks to him on the phone and has to make up a lie when he wants to have a sleepover.
David was possibly one of the two boys seen at Stairway to Heaven, where ALF dreamed that if he didn't exist in the Tanners' home, then Brian would be able to have his friends come over and play in the pool in the backyard. This was all affordable due to Willie's success in his job, a fortune won by a lottery ticket, and only a few expenses. However, due to ALF existing with the Tanners, they almost only have as much money as a normal family.