Black Widow (Spy)

Black Widow did appear in the comics tie-in to.

Biography
Black Widow was an agent of HYDRA who got disenchanted with Baron Strucker's goals, so she snuck information to NATO and S.H.I.E.L.D., and helped the Avengers to infiltrate into Hydra's base. When Hawkeye blew the team cover, Strucker revealed that he already knew about Black Widow's betrayal. After defeating Strucker, Hawkeye apologised with Black Widow for mistrusting her and they grew attracted to each other.

Some time later, when Hawkeye and Black Widow stopped Whirlwind together, she found an inertial field generator on Whirlwind's persona. As it was A.I.M technology, Black Widow tracked an A.I.M. facility in Northern Canada, but was captured when sending a message to the Avengers. Hawkeye went to help her, accompanied by Falcon, Scarlet Witch and Vision.

Hwkeye found Black Widow safe and sound... and kissing an A.I.M. scientist. When the Avengers attacked the facility, Black Widow and the scientist escaped followed by Hawkeye. Black Widow then explained that the scientist was her husband Alexi Shostakov, who she believed dead until she recognised his handiwork in Whirlwind's device. Black Widow wants to take Alexi away from A.I.M. and Hawkeye lets her go, later telling Vision that she was never there.

In the Comics
Natasha was a russian spy who manipulated Hawkeye to steal Tony Stark's technology, but she later changed sides and became an Avenger.

Her husband's name is Alexei, indeed, and she believed him dead, but instead of a scientist, he was a pilot and became the Red Guardian, the russian answer to Captain America.