How a modern-day James Bond went from uncovering political assassinations to penning the Trump dossier that's enraging Republicans

• President Donald Trump's first year in office has been plagued by parallel Russia investigations - one led by special counsel Robert Mueller and the other led by the House Intelligence Committee.
• Behind both of these investigations stands British spy Christopher Steele, and the dossier he authored during the 2016 election about Trump's ties to Russia.
• The elusive MI6 agent has a fascinating life, from his time uncovering political assassinations to his current role as a defining figure in the Russia probes.

The life of Christopher Steele reads like the script of an international spy thriller.

From the shores of Yemen to MI6 offices in Moscow and London, the British spy amassed an impressive career before he compiled the infamous yet seminal dossier about then-US presidential candidate Donald Trump's ties to Russia in 2016.

The elusive agent's credibility and expertise have come under increasing scrutiny over the last several months.

While the explosive claims about Trump's collusion with Russia that Steele makes in his dossier have yet to be independently corroborated, little by little, investigators are confirming bits and pieces of the document. Now, a second dossier has emerged that reportedly came to many of the same conclusions Steele did.

Although he has been maligned as a political operative who compiled the dossier for partisan gain, it is clear from his activities that over time, the dossier became a deeply personal matter for Steele. He saw its completion as a matter of national security for both his native United Kingdom and the United States.

Here's a look at how Steele became a vital intelligence source on both sides of the Atlantic - and a defining figure in the Russia investigation in the process: