<Li> Det . John Clark Sr. -- John Clark Jr. 's father . An average detective from a low crime precinct mutually despised by Sipowicz , who called him `` Dutch Boy '' in reference to a plaster marketing statue he once shot in the dark thinking it was a suspect with a gun . He threw his son out of the house when John Jr. decided to work at the 15th with Andy ; his partner and he later worked a case with Clark Jr. and Andy that revealed Clark Sr. 's by - the - book approach and hyper - sensitivity to his son being anything like Andy . ( In fact , Andy was much more the kind of detective Clark Jr. wanted to be , which is why he chose to transfer to the 15th when he earned a detective 's shield and pick of assignments . ) Clark Sr. later got busted for sleeping with a prostitute and let his son face the IAB accusation and potential discipline until Andy told him Clark Jr. was on the verge of being fired , which caused Clark Sr. to confess . After this , Clark Sr. began drinking heavily and became an IAB informant , which nearly ruined John 's career at the 15th . His actions helped lead to the campaign by Officer Laughlin against Clark Jr. , who finally told his father to stop making bad decisions on his behalf and stop drinking so much . A depressed Clark Sr. later committed suicide , which sent his son into a long depression of his own . Played by Joe Spano . </Li>
who played john clark sr on nypd blue
Joe Spano