Complex sentence: There, he developed into one of Spain's most important footballers during the 90's, being an instrumental piece in Atlético's historical double in 1995--96, with goals and assists alike.
Split into simpler sentences: There, he developed into one of Spain's most important footballers during the 90's. Kiko was an instrumental piece in Atlético's historical double in 1995--96, with goals and assists alike.