Mano of the Fatal Five, and correct on the last two.
Holding a DQ.
IQ1: Are you aka Shadow Lass of the Legion of Super-Heroes?
IQ2: Were you a physicist who figured out much of the math behind electromagnetism?
IQ3: Are you known for your early work on radio transmission?
IQ1: Did you play Peter Petrelli in Heroes?
IQ2: Did Keanu Reeves play you in a 1995 film where you carried data in your head?
IQ3: Are you the Centaurian ambassador to Babylon 5?
DQs:
SCAdian, you duplicated KO’s question, so take another.
#2. I am not Johnny Mnemonic. Take 2 DQs for the others.
Correct, James Maxwell (of Maxwell’s equations fame) and correct.
DQ: Born prior to 1900?
holding one DQ.
DQs:
What is it with all these people around here asking questions while I’m typing? 
DQ: Known for science?
Milo Ventimiglia, correct, Llondo Milare
DQ: Born east of the Mississippi?
2 DQs remaining
DQs:
IQ1: Did you help survey the western border of Delaware?
IQ2: Did you develop a mechanical reaper?
IQ3: Were you really Cornelius McGillicuddy?
Previous IQs:
Did Richard Harris play you in one of his final roles? - Marcus Aurelius in Gladiator.
Did you have a slave named Cicero? - Maximus (Russell Crowe), ditto.
Were you Sherlock Holmes’s rotund brother? - Yes, Mycroft Holmes.
DQs:
Born before 1800?
Businessman/entrepreneur/inventor?
IQs:
Were you a key leader in a lunar rebellion?
Were you the computer who helped him?
Did the actor who played you have makeup for a bigger nose and longer hair?
IQ1: Are you known for your Doctrine?
IQ2: Are you known for your Code?
IQ3: Did you measure the charge of an electron in a drop of oil?
DQs:
Charles Mason. (He and Dixon surveyed the southern and western borders of Delaware before continuing west along the Maryland/Pennsylvania line.)
Correct.
Connie Mack.
DQ1: Invented something?
One DQ reserved.
DQs:
IQ: Were you a financier involved in the creation of General Electric and US Steel?