A woman who turns up whenever somebody has just been humiliated, offers them work, and is running something nobody has fully explained yet.
Valentina is a structural character: she exists to connect films that were made years apart. Julia Louis-Dreyfus plays her as someone who is enjoying herself enormously and telling the truth about roughly half of what she says, which makes her hard to place and easy to watch.
By Thunderbolts the shape is clear. She has been recruiting damaged people individually, off the books, for years, and the film is what happens when they all meet each other and compare notes.