Who is the wizard who killed Harry Potter's parents?

Lord Voldemort (Tom Riddle Jr.) killed Lily and James trying to get to Harry when he was baby due to the part-heard prophecy:

"the one with the power to vanquish the dark lord approaches...born to those who have thrice defied him,born as the seventh month dies...and the dark lord will mark him as his equal, but he will have power the dark lord knows not... and either must die at the hand of the other for niether can live while the other survives... the one with the power to vanquish the dark lord will be born as the seventh month dies...."

Voldemort's informant (Severus Snape) only heard the lines in bold, which means he didn't know that he fulfilled the prophecy by marking Harry as his equal.

A lot of people lead indirectly to their deaths, for instance, Sirius Black convinced James and Lily to make Peter Pettigrew their Secret Keeper instead of him because he was the obvious target. However, Sirius was unaware that Peter was actually a spy for the Death Eaters. Making him their secret keeper allowed Pettigrew to betray their location to Voldemort, so he could kill them.

Sirius Black got falsely accused of doing what Pettigrew did though, because everyone else thought he was their Secret Keeper.