Oliver Jonas Queen is Chloe Sullivan's husband as well as the billionaire owner and CEO of Queen Industries, who also serves on a team of heroes as avigilante archer, Green Arrow. As Green Arrow, Oliver dresses in green and black and utilizes a variety of arrows and gadgets for many forms of defense.
When Oliver descended into depression after learningLionel killed his parents, he turned towards a lifestyle of women, drinking, and partying. He then again abandoned his Green Arrow duties and spent many months making the gossip pages. He eventuallydecided to get his life back on track, thanks to Chloe Sullivan's intervention.
In 2009, Oliver Queen discussed merging Queen Industries with LuthorCorp. However, the day he was to discuss the merger with the LuthorCorp Board of Directors, every member was killed in an explosion. It is unclear how much influence or stake Oliver currently holds in the company. 
In late 2009, Oliver discovered a prostitute and street fighter named Mia Dearden. Seeing her fighting skills, Ollie took her under his wing and got her off the streets, training her in martial arts with the hope that she could be an ally for his team of metahuman superheroes.
Recently, due to the frequent bad press about costumed heroes being deemed vigilantes, and to the loss of his true love Chloe, Oliver revealed to the public that he is Green Arrow to prove the media wrong and hopefully be reunited with the woman he loves.
For a more detailed look at Oliver Queen, go to his page on Smallville Wiki, here.