Satan has appeared as an antagonist in the TV series "Touched By An Angel" and often took the form of human beings so as to try and tempt people from the path of God - his efforts were opposed by the angelic heroes of the series, who often had to help people regain faith in order to ward off Satan's influence.
Although the majority of the series was based on personal struggles rather than supernatural threats, a few episodes did show Satan to be the main instigator of evil - such as when he tried to corrupt a group of religious people into adopting a racist doctrine via disguising himself as a preacher.
Satan, by his very nature, could also be argued to be involved behind the scenes in every one of the series conflicts or tragedies - though he only appeared personally in a few episodes. He was portrayed in the series by Mandy Patinkin.
Appearances In The Show
"In The Name Of God"
Satan manifested as an authority figure in a small community and used his influence to form a white supremicist group that twisted faith into aggression - this angered Tess to the point she temporary lost her angelic powers and was replaced by another angel named Sam. However after reconciling with God, Tess joined the other angels in a raid of the area Satan was corrupting, where they revealed his true nature to his would-be-pawns and ultimately foiled his plan.
Satan appeared as a smart driver who tempted Monica after the angel's faith was momentarily shattered upon seeing a bombing that caused a number of deaths - trying to play on her insecurities so as to convert her to his cause and abandon God. Ultimately Monica's own faith proved stronger than Satan's temptation and he left.
Satan is depicted as a master manipulator with a talent for words, he is said to rely heavily on his reputation but has his pawns do all the dirty work - when confronted Satan will try to turn the tables on his opponents and gain possession of a would-be-victim via trickery or falsehoods, yet when his true nature is revealed he quickly leaves as he can not stand to be among those of strong faith.
Satan seems to view freewill as a curse, as he noted to Tess once, trying to control others and stealing their gifts and ultimately their lives - subtly leading them on the path of ruin.
Presumably Satan also exhibits the same pride and wrath as the Biblical Lucifer, as well as any number of vices found in the Seven Deadly Sins.
Satan is depicted as being a powerful supernatural being who can appear as almost anything he desires - however when dealing with humans he is limited to utilizing their own free-will against them, exploiting pre-existing hate, fear or anger in order to manipulate them into breaking away from God and the postive side of life.
Satan is hinted at being omnipresent but by no means omnipotent - in fact it is established fairly early on that Satan will be left with no choice but to abandon a would-be-pawn or victim if he or she personally asks God for protection (in a broader term faith seems to be Satan's main weakness, the stronger the faith the less power he can hold over others - which explains why he tries so hard to corrupt others).