Thaddeus, a distinguished, long-neglected appellation, has several areas of appeal: a solid New Testament legacy, a nice antique feel, and the choice of several more modern nicknames and international variations. In the USA, it has started picking up some momentum: in 2013, it reached Number 797 and did even better in 2014 at #732. In the UK it is practically unheard of: in 2013 it was given to 5 children, placing it well outside the Top 3000.
In the Bible, Thaddeus was one of the original Twelve Apostles, who is referred to variously as Lebbaeus, whose surname was Thaddaeus, as Judas the son of James, and as Judas, not Iscariot-- many believing that Thaddeus was the surname used to distinguish him from the treacherous Judas Iscariot.
Thaddeus has made any number of screen appearances ranging from Spongebob Squarepants to Police Academy to Get Smart (it was the given name of the Chief) to Harry Potter. As Tadzio--the Slavic version--he played a leading role in Thomas Mann's Death in Venice.