Frank Westen makes his first appearance on Jupiter the 7th episode in, Mike's imagination, while Michael is under drugs. He was a compulsive gambler and alcoholic who frequently beat them. The only one to ever stand up to him was Michael himself, who would oftentimes take the blame and abuse in place of his younger brother Nate. Frank was also apparently quite cheap as he would make Michael fake seizures while stealing spark plugs from one of his neighbors. His (abusive) life as a family man, lead to a number of things that shaped Michael into the man he is today. For one, Madeline would forge his signature, under the pretence that Frank did it himself, and sign her son in the army so that he could get a better life; this sparked a number of events which lead to Michael becoming a spy and getting burned.
Despite all of his vices, Frank Westen really loved his family and wished to actually be considered a part of it. He would however, show this in very obscure ways. For instance, rewiring Madeline's car so that if it ever broke down, he would be the only one who could fix it. Although none of that helped as Michael hated him so much that he did not attend his funeral, and only visited his grave years later on the insistence of his mother.
As the years passed by, Frank became more mellow and started to truly regret his actions towards his family. According to Anson Fullerton when he pretended to be their therapist, he was quite the talker and actually cried at some their sessions. Although "the whisky helped", Frank would talk how proud he was of his oldest son standing up to him, while protecting his mother and younger brother; also of the things he said.
Apparently, Michael's overall cautious and curious nature had been passed down to him by his father; as Frank had become suspicious of Anson and his interest in his son and was killed for it.
Frank appeared to Michael in a drug-induced hallucination in Psychological Warfare, his appearance helped Michael realize how strong he really is and ultimately saved Michael's life and preserved his cover.
Frank Westen was killed from a heart attack by Anson Fullerton when he became too suspicious about the man's interest in his son.