HBO is looking to expand its relationship with one of its proven hit-makers by teaming him up with one of Hollywood’s biggest stars.

Nic Pizzolatto and Robert Downey Jr. are in talks for a drama project, with the “True Detective” creator attached to write and the “Iron Man” actor attached to star, sources tell Variety.

HBO and reps for both Pizzolatto and Downey Jr. declined to comment.

Plot details are scarce, but insiders say the project is based on Downey Jr.’s “Perry Mason” reboot, which he had been developing as a feature film at Warner Bros. for several years. Pizzolatto, Joe Horacek, Downey Jr., and his producing partner and wife, Susan Downey, of Team Downey will serve as exec producers.

Sources indicate the project will be a series, rather than a TV film, and that the project has been gestating at HBO since as early as May.

This project would mark Downey Jr.’s first starring role on television, aside from his “Ally McBeal” stint in the early 2000’s, before he re-surged to became a box-office superstar.

Downey Jr. has wanted to do some sort of “Perry Mason” project for some time, having originally set it up at Warner Bros. as a film back in 2011. The film never found its footing and after his other lawyer-driven pic “The Judge” had mixed results at the box office, the studio and Team Downey thought that television was a better platform for it. “Perry Mason,” starring Raymond Burr, ran on CBS from 1957 to 1966.

With a third season of “True Detective” still in flux, this potential series keeps Pizzolatto in the HBO fold with a new high-profile project, given his recent overall deal with the premium cabler, which lasts through 2018.

For Downey Jr., the project not only marks his big foray into TV on the screen, but also as a TV producer. The “Iron Man” star put a drama into development with Showtime in 2014, though it never come to fruition.

Both Downey Jr. and Pizzolatto are repped by CAA. Pizzolatto is also repped by Anonymous Content.