Paul Dano (There Will Be Blood) There Will Be Blood
Paul Dano was originally cast only as Paul Sunday — a one-scene role that exits the film at minute nineteen. When the actor playing Eli Sunday was fired after two weeks of shooting, Anderson asked Dano to take on the far larger role of Eli as well, giving him fewer than four days to prepare opposite an actor who had spent over a year building his character.
Dano replaced Kel O'Neill after two weeks of filming
Kel O'Neill was originally cast as Eli Sunday. After two weeks of production, Anderson decided O'Neill's performance was not working and fired him. Rumors circulated that O'Neill had been intimidated by Day-Lewis, but Anderson, Day-Lewis, and O'Neill all denied this. Day-Lewis stated: "I absolutely don't believe that it was because he was intimidated by me." O'Neill attributed the dismissal to a poor working relationship with Anderson and his diminished interest in acting. (collider, indiewire)
Anderson restructured the characters as twins and asked Dano to play both Paul and Eli.
"On There Will Be Blood I was cast at the last minute. I had 3 1/2 to 4 days to get ready for the first day. That was just guts and instinct, not a lot of preparation." — Paul Dano, IndieWire
The imbalance between actors became part of the film's texture
Dano's minimal preparation time opposite Day-Lewis's months of character work created a visible power asymmetry on screen. Dano — visibly younger, less physically imposing, working with far less rehearsal — appears genuinely overwhelmed in certain scenes, and that quality mirrors the dynamic between Eli and Plainview. The character is outmatched by the man across from him, and the actor is outmatched by the actor across from him. The two registers reinforce each other.
"I was just going holy sht, he's so powerful." — Paul Dano, on working with Day-Lewis, All The Right Movies*
"I was in good hands with Paul and Daniel, I felt I had to cut loose and go for it." — Paul Dano, SlashFilm
Dano built Eli's preaching style from the script rather than historical models
Rather than studying specific televangelists or period preachers, Dano constructed Eli's performance from Anderson's dialogue, noting that the character would not have had access to radio, television, or other preachers to imitate.
"I think he invented himself... quite a bit of an actor... created a persona at a very young age." — Paul Dano, Fresh Air (2008)
"His words and the language were so wonderful that a lot of it... came directly from the words." — Paul Dano, Fresh Air (2008)
The approach produced a preacher who feels self-taught rather than polished — theatrical enough to hold a congregation but raw enough to crack under pressure, which is exactly what happens in the bowling alley finale when Eli's cadences collapse into desperation.
The slapping was mutual and partly accidental
The film's two key confrontation scenes — Plainview beating Eli in the mud, and Eli slapping Plainview during the baptism — were shot on consecutive days. Dano described the experience with characteristic understatement.
"Daniel slapped me around one day and then the very next day I got to get my revenge." — Paul Dano, Fresh Air (2008)
During the baptism scene, Dano accidentally struck Day-Lewis with full force: "I forgot and I just slapped the hell out of his face on the very first take." The physical reality of the encounters — two actors genuinely hitting each other — gives the scenes their visceral charge. (freshairarchive)