...And your daughter...there's a big question mark over her head... -Eddie Nigma, Robin 113
Real name: Edward Nashton
Alias: Edward Nigma.
After Arthur's death, Steph went to question Eddie about her father. He was unable to give a straight answer, despite the fact she promised to give him the keys to Arthur's safe deposit box. (He's mentally unbalanced, poor guy) This naturally made Steph angry and she beat the crap out of him, then left. He was mildly interested in what her deal is. But not enough to do anything about it apparently.
Read more about the Riddler here