One of the hardest working (and oldest) directors in Hollywood, Clint Eastwood, began production on his Hoover biopic, J. Edgar, last month – and now two more talents have signed on to play supporting roles in the period drama, which is being headlined by Leonardo DiCaprio as the titular FBI founder.

Burn Notice star Jeffrey Donavan (who previously worked with Eastwood on Changeling) will play the role of Robert Kennedy in J. Edgar. Miles Fisher is set for the part of Agent Garrison, an FBI employee who interviews DiCaprio’s Hoover throughout the film.

Robert Kennedy served as an advisor to his sibling, John F. Kennedy, during his short-lived time as president, and remained a highly active figure up until his assassination in 1968. Donavan confirmed his involvement via Twitter yesterday (note: he’s since clarified “Not ‘cars’ meant: ‘cast'”), and his role is indeed one that’s ripe for drama – seeing as there was a fair degree of animosity in general between the Kennedy clan and Hoover (partly due to J. Edgar’s detailed file about the family’s Mob ties).

Deadline has the scoop on Fisher, whose career was largely restricted to appearances on TV shows like Mad Men and Gossip Girl prior to his snagging a lead role in the upcoming Final Destination 5. Fisher also starred in the short William Morris-Endeavor (WME) satire “Pinkberry: The Movie”, a shot-on-the-fly clip that pokes fun at the commercial influences of Hollywood studio productions.

You can check out that amusing video below, but note – it contains some NSFW language:

J. Edgar features quite the motley crew, including DiCaprio as Hoover; The Social Network‘s Armie Hammer as the FBI head’s rumored secret lover, Clyde Tolson; Naomi Watts as Helen Gandy, Hoover’s lifelong secretary; and Dame Judi Dench as his mother.

Rounding out the cast are individuals like Josh Lucas as the aviator legend, Charles Lindbergh; Stephen Root (No Country for Old Men) as Arthur Koehler, a wood specialist who played a pivotal role in the investigation of the Lindbergh baby kidnapping; Justified‘s Damon Herriman as the convicted Lindbergh baby killer, Bruno Hauptmann; and Ken Howard as U.S. attorney general Harlan F. Stone.

Oscar-winner Dustin Lance Black’s J. Edgar screenplay will reportedly examine Hoover’s life following the establishment of the FBI on through to his death in the 1970s. The film should be the sort of complex character study that Eastwood excels at as an auteur, and is already shaping up to be a potential awards season contender this fall. For those who couldn’t care less about such matters, J. Edgar at least looks to be an interesting and well-made drama about the life of a very complicated, real-life historical figure.

Look for J. Edgar to arrive in theaters during the second half of 2011.

Source: Jeffrey Donovan, Deadline