To be honest, we aren't actually told that much about Sam in terms of specific details. His account, however, does allow us to infer the kind of person that he is and he does tell us something about his past, in particular the kind of work he has been involved in. The allusions that he makes to the Bible and the way that he knows the origin of the word paradise indicates that he is an educated man. His sadness and the way that the communal garden quickly devolves into every man for himself shows that he is somebody that cares deeply about integration and social equality, and he is clearly a talkative person who likes to get to know people.
Sam tells us he is 78 and that he likes to challenge prejudices, talkign to people so that they can see he is "friendly, no matter what they've heard about whites or Jews." His goal is "Sewing up the rips in the neighbourhood," which is of course very similar to what he used to do before:
I used to try to patch up the whole world. For thirty-six years I worked for different groups, promoting world government, setting up conferences on pacifism, raising money, stuffing envelopes.
Now, Sam has "switched battlefields," trying to continue the same work but focusing on this communal garden.