Meet Robert Mueller, the former FBI director and tenacious investigator now leading the Trump-Russia probe

It's been almost five months since Robert Mueller became the special counsel in the investigation into Russia's interference in the 2016 elections and whether President Donald Trump's campaign colluded with the Kremlin.

In Washington, Mueller has a reputation for being a tenacious investigator. Both Republicans and Democrats welcomed his appointment in May with bipartisan backing.

The increasing breadth of his investigation, however, has irked some Trump supporters.

Mueller's colleagues, meanwhile, say he has proven his bipartisan bona fides over the years. After all, he served under both Republican and Democratic presidents as FBI director and as an attorney in the Department of Justice.

As the probe into Trump and his associates heats up, here's a look at Mueller's history: