The actress is Margot Robbie. She plays Harley Quinn I'm Suicide squad. Puddin is a cute nickname that Harley gave Joker since they're technically dating? Lmao. I hope I'm right
I think they over romanticized Harley and Joker in Suicide Squad xD In the comics, Harley looooves Joker and will do anything for him, however he doesn't feel the same and would gladly give her up for his own benefit. He abuses her and sends her to do his deadly dirty work. It's not a dating relationship but more of a one-sided crush kinda thing.
While Joker does treasure Harley for her devotion to him, like I said, he doesn't really have romantic feelings for her (as depicted somewhat in Suicide Squad).