Estate of Tank, 938 N.W.2d 449

Decedent Russell Tank (d. 2016) executed wills in 2001, 2004, and 2012; the 2012 will revoked prior wills and named longtime tenant/neighbour Jason Bender sole heir and personal representative, expressly disinheriting Russell’s four adult children (Arlo, Renny, Sherri, Gina).
Bender had farmed Russell’s land since 2002 at below‑market rent, became Russell’s attorney‑in‑fact in 2009, assisted with errands and nursing‑home placement, and held large sums of Russell’s cash (some buried on the farm).
Children petitioned to invalidate the 2012 will alleging lack of testamentary capacity, insane delusions, and undue influence; each side retained a psychologist (Dr. Swenson for Children — opined delusional disorder and dementia; Dr. Tranel for Bender — disagreed about delusions).
The circuit court granted summary judgment for Bender on all claims, concluding Russell had testamentary capacity, was not afflicted by an insane delusion material to the will, and there was no evidence of improper disposition by Bender to exert undue influence.
On appeal, the Supreme Court of South Dakota affirmed summary judgment as to testamentary capacity and insane delusion, reversed as to undue influence only for Sherri, and affirmed summary judgment as to undue influence claims by Arlo, Renny, and Gina.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Testamentary capacity	Russell’s delusional disorder and dementia prevented comprehension of the meaning/importance of his relationships with his children, so he lacked capacity when executing the 2012 will	Russell understood his property, knew his heirs, and clearly expressed his intent to disinherit his children	Affirmed: Russell had testamentary capacity; knowledge of heirs and intended disposition satisfied the statutory test
Insane delusion	Russell’s lifelong paranoia/delusional disorder rendered him incapable of rationally perceiving his relationships with his children and caused the disinheritance	No fixed, specific delusional belief was shown that materially affected the will’s terms	Affirmed: No evidence of a specific insane delusion that materially affected the 2012 will
Undue influence	Circumstantial evidence (below‑market rent, control as attorney‑in‑fact, possession/handling of cash, changed beneficiary from 2001 to 2004) shows Bender had disposition and produced a result showing undue influence	Bender lacked improper disposition; consistency with prior wills and Russell’s personality weigh against susceptibility	Mixed: Reverse summary judgment as to Sherri (material fact issues exist); affirm summary judgment as to Arlo, Renny, and Gina (no causation between Bender and their disinheritance)

Stockwell v. Stockwell, 790 N.W.2d 52 (S.D. 2010) (knowledge of heirs supports finding of testamentary capacity)
In re Estate of Pringle, 751 N.W.2d 277 (S.D. 2008) (capacity assessed over a reasonable time surrounding execution)
In re Estate of Schnell, 683 N.W.2d 415 (S.D. 2004) (definition and effect of insane delusion on wills)
In re Estate of Berg, 783 N.W.2d 831 (S.D. 2010) (will invalid only if delusion materially affected terms)
In re Estate of Dokken, 604 N.W.2d 487 (S.D. 2000) (burden on will challenger to prove lack of capacity)
Neugebauer v. Neugebauer, 804 N.W.2d 450 (S.D. 2011) (below‑market transactions can support inference of undue influence)
In re Blake's Estate, 136 N.W.2d 242 (S.D. 1965) (consistency between wills may negate undue influence)
Metz v. (Estate), 100 N.W.2d 393 (S.D. 1960) (undue influence typically established by circumstantial inferences)