Villanueva, 29, joins the Cubs after pitching the last seven seasons with Milwaukee (2006-10) and Toronto (2011-12). The versatile Villanueva has made 56 starts and 245 relief appearances during his major league career, going 33-35 with six saves and a 4.26 ERA (311 ER/657.1 IP) in 301 big league outings. In his most recent two seasons with the Blue Jays, Villanueva made 29 starts and 42 relief appearances.
Last season, Villanueva carried a 7-4 record and a 3.10 ERA (34 ER/98.2 IP) in 33 appearances (11 starts) through the end of August before struggling during the season's final month with a 0-3 record and an 8.10 ERA (24 ER/26.2 IP) in five starts in September. Overall in 2012, Villanueva went 7-7 with a 4.16 ERA (58 ER/125.1 IP) in 38 appearances (16 starts) with the Blue Jays.
Villanueva made his major league debut with Milwaukee in 2006 and became a big league mainstay by the 2008 season. He set a career high with 64 appearances in 2009 and averaged a career-best 11.4 strikeouts per nine innings in 2010, his lone season pitching exclusively in relief, before joining the Blue Jays in 2011. Villanueva last season set career highs with 125.1 innings pitched, 16 starts and 122 strikeouts.
Overall in his career, Villanueva has limited opponents to a .248 batting average against and a .315 on-base percentage against. He has averaged 7.8 strikeouts and 3.1 walks per nine innings.
A native of Santiago, D.R., Villanueva originally signed with San Francisco as a non-drafted free agent in 2002. He was traded to Milwaukee just days prior to the 2004 season and was traded to Toronto during the 2010-11 offseason.
Castillo went 0-1 with a 7.88 ERA (14 ER/16.0 IP) in 13 relief outings for the Cubs last season.